Pituitary and gonadal hormone-dependent and -independent induction of follicle-stimulating hormone receptors in the developing testis

The number of FSH receptors increases during testicular development in several species of mammals. Hypophysectomy and hormonal replacement were performed to identify the factors that induce developmental changes in testicular FSH receptors. Male rats of the Wistar/Tw strain were hypophysectomized at 9, 16, 23, or 30 days or 3 months of age. These rats were killed 10 days after surgery along with intact control rats, and the testes were removed for receptor assay. A group of intact rats was killed on the day of surgery as initial controls. All of the hypophysectomized immature rats showed a higher density of FSH binding (FSH binding per unit weight) and a lower total FSH binding (FSH binding per two testes) compared with each of the matched intact control rats. In contrast to FSH binding, not only the total LH binding but also the density of LH binding were invariably lower in the hypophysectomized rats than in the intact control rats. Unlike hypophysectomy at other immature ages, surgery at 9 days of age was followed by significant increases in testicular weight, density of FSH binding, and total FSH binding compared with those values in the initial control rats. There was no significant effect of hypophysectomy on total FSH binding in adult animals, in contrast to the marked decrease in total LH binding. When male rats hypophysectomized at 25 days of age were injected with FSH for 5 days beginning on the 11th day after surgery, dose-dependent increases in total FSH binding and testicular weight were observed. Testosterone treatment induced an increase only in the total FSH binding, but its effect was less potent. Scatchard plot analyses of the binding suggested that changes in FSH binding with age, after hypophysectomy, and after hormonal administration were due to changes in the number of binding sites. Plasma FSH concentrations in all postoperative rats were below or at the level of detectability, indicating that hypophysectomy was successful. In normal immature rats, a significant increase in the plasma FSH level was detected only from 9-19 days of age, in contrast to the continuous increase in total FSH binding during testicular development. These results suggest that FSH and testosterone act as hormonal factors to induce an increase in the number of FSH receptors in the developing testis. Other factors that are independent of pituitary and sex hormones may also contribute to FSH receptor induction.     

Plasma 5 alpha-dihydrotestosterone and testosterone in the bullfrog, Rana catesbeiana: stimulation by bullfrog LH.

Effects of purified bullfrog (Rana catesbeiana) LH and FSH on plasma levels of the androgens, testosterone (T), and 5α-dihydrotestosterone (DHT), were studied using adult male bullfrogs. Rana LH was considerably more potent than Rana FSH in stimulating increased plasma androgen levels in hypophysectomized and intact animals. Simultaneous injection of Rana FSH or ovine PRL with Rana LH, over a 10-day period, did not alter the LH-induced increase in plasma androgens. More DHT than T was present in plasma after LH injection. Castration abolished plasma DHT and greatly reduced plasma T. Results indicate that DHT is a major testicular steroid, and that testicular androgen secretion is stimulated primarily by LH in the bullfrog.     

Transferrin and sulfated glycoprotein-2 messenger ribonucleic acid levels in the testis and isolated Sertoli cells of hypophysectomized rats

Both FSH and testosterone act on Sertoli cells in the testis. It is possible that the action of these hormones on Sertoli cells results in an increased capacity for the cells to carry out their prescribed functions, among which are the synthesis and secretion of specific glycoproteins. Changes in the testicular levels of two specific mRNAs in hypophysectomized hormone-treated rats were determined by solution hybridization to cRNA probes. The mRNAs coding for transferrin and sulfated glycoprotein-2 (SGP-2), both of which are secretion products of Sertoli cells, decreased dramatically in the testis of hypophysectomized rats that were maintained for 20 days untreated with hormones. If hypophysectomy was done to rats at 20 days of age, daily injections for a subsequent 20 days with FSH or FSH in combination with testosterone partially maintained both transferrin and SGP-2 mRNA levels. Testosterone alone was ineffective in 20-day-old rats. In contrast, if hypophysectomy was performed on 40-day-old rats, daily injections of testosterone alone or in combination with FSH were most effective in maintaining higher levels of the specific mRNAs. When the Sertoli cells from rats hypophysectomized at 20 days of age were placed in cell culture, FSH again was most effective in the stimulation of transferrin mRNA above control levels. However, when the Sertoli cells from the rats hypophysectomized at 40 days of age were placed in culture, FSH was slightly stimulatory, but testosterone had no effect on the transferrin mRNA levels. Neither FSH nor testosterone affected the levels of SGP-2 mRNA in the cultured cells regardless of the age of the animal at the time of hypophysectomy. Additional in vivo studies were done in which the rats were hypophysectomized at 20 days of age, allowed to regress for 17 days, and then injected daily with hormones for 3 days. The levels of transferrin and SGP-2 mRNA in this experiment were stimulated by FSH alone or by a combination of FSH and testosterone to an extent similar to that in the cultured cells. These studies showed that FSH is most important in the younger rats and testosterone is most important in the older rats in the maintenance of specific mRNA levels. In addition, the level of stimulation observed with either hormone is different depending on whether the hormone is given in culture or in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)     

In vivo responses of female snakes (Natrix fasciata) and female turtles (Chrysemys picta) to ovine gonadotropins (FSH and LH) as measured by plasma progesterone, testosterone, and estradiol levels

Changes in plasma progesterone, testosterone, and estradiol-17β in serially bled female snakes (Natrix fasciata) and female turtles (Chrysemys picta) in response to single iv injections of ovine LH or FSH were measured by RIA. In snakes, both FSH and LH increased the levels of all three steroids in plasma, though considerable individual variation in response to either hormone was encountered. The apparent differences in the responses to the gonadotropins may have been due to differences in the stage of follicular development in different animals. In contrast, in female turtles, ovine FSH was clearly most active in stimulating steroid (testosterone and estradiol) synthesis, although LH has a consistent, though minor, stimulatory effect on estradiol secretion 30 min after injection. Neither hormone stimulated progesterone secretion at the time of year tested. In snakes, but not in turtles, it was possible to correlate preinjection plasma levels of estradiol with the stage of follicular development, high levels of hormone being found in animals with large follicles and low levels in animals with small follicles.     

Effects of pure FSH and LH preparations on the number and function of Leydig cells in immature hypophysectomized rats

The effects of pure FSH and/or LH preparations on the number of Leydig cells and their function in immature hypophysectomized rats have been investigated. As a result of hypophysectomy at the age of 17-18 days, the number of recognizable Leydig cells per testis decreased, as did the steroidogenic capacity in vivo and in vitro. Treatment with 64 micrograms FSH on both 22 and 23 days of age, did not affect the number of recognizable Leydig cells. In contrast, two injections of LH (10 micrograms) caused a sixfold increase in the number of Leydig cells, but had a negative effect on spermatogenesis. These stimulatory and inhibitory effects of LH diminished when FSH was added. Treatment with FSH for 7 days caused a twofold increase in the number of Leydig cells when compared with hypophysectomized controls. 3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) and esterase activity in Leydig cells also increased under the influence of FSH. The pregnenolone production per Leydig cell in the presence of 5-cholesten-3 beta,22(R)-diol (22R-hydroxycholesterol) as substrate showed a sevenfold increase. Plasma testosterone levels 2 h after injection of human chorionic gonadotrophin in intact rats and hypophysectomized FSH-treated rats were the same. Following LH treatment for 7 days, the number of Leydig cells proved to be 11 times higher, and 3 beta-HSD and esterase activity were not different from intact controls. The testicular pregnenolone production was four- to fivefold higher when compared with untreated hypophysectomized rats. However, pregnenolone production per Leydig cell in LH-treated rats was only slightly different from the hypophysectomized controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differential effects of FSH and testosterone on the maintenance of spermatogenesis in the adult hypophysectomized rat

In order to clarify further the role of FSH in the maintenance of spermatogenesis, adult rats were treated with purified human FSH (2 X 5 IU/day per rat), testosterone (1.5 cm silicone elastomer implant) or a combination of both hormones for 2 weeks following hypophysectomy. After hypophysectomy alone, no elongate spermatids were observed and the numbers of pachytene spermatocytes and round spermatids observed were reduced when compared with untreated controls. Testosterone supplementation alone qualitatively maintained the formation of elongate spermatids in most seminiferous tubules, whilst in FSH-treated rats increased numbers of round spermatids and pachytene spermatocytes were observed when compared with hypophysectomized animals. Formation of elongate spermatids, however, did not occur under FSH treatment alone. A combination of FSH and testosterone treatment maintained spermatogenesis in an almost quantitative fashion. Numbers of pachytene spermatocytes and round spermatids were maintained at about 80% of levels seen in intact control animals. Treatment with FSH or testosterone alone maintained testis weights at significantly higher levels than those seen in hypophysectomized controls (FSH, 0.79 +/- 0.05 g; testosterone, 0.81 +/- 0.07 g; hypophysectomized, 0.50 +/- 0.04 g). Animals treated with FSH and testosterone showed testis weights 20% below control values (1.22 +/- 0.05 vs 1.51 +/- 0.06 g; P less than 0.05). No increases in intratesticular or intratubular androgen concentrations or in testosterone: dihydrotestosterone ratios were observed in any of the hormone-treated groups when compared with hypophysectomized controls. In all hypophysectomized animals testicular androgen concentrations were reduced to less than 5% of control values. The results obtained in this study suggest that FSH is involved in the maintenance of spermatogenesis in the adult rat and that the effects of FSH are not mediated through changes in intratesticular androgens. Low levels of testosterone in combination with FSH can almost quantitatively maintain spermatogenesis in adult rats.     

Effect of bullfrog LH and FSH on newt testes under different temperatures

Environmental temperature plays important roles for amphibian gonadal function. In this study, we examined the responses of testicular tissue of adult male newts (Cynops pyrrhogaster) to amphibian gonadotropins both in vitro and in vivo under different temperatures. When minced testes were incubated in vitro at different temperatures (8-37 degrees C) under an atmosphere of 95% O(2)-5% CO(2) for 3h with bullfrog luteinizing hormone (LH) or follicle-stimulating hormone (FSH), LH stimulated testosterone production more than FSH. The testosterone production increased as the incubation temperature increased. Hypophysectomized newts were injected with bullfrog LH or FSH and maintained at 8 or 18 degrees C. In the 18 degrees C group, the testicular weight of the hypophysectomized control decreased when compared with that of with the intact control. The testicular weight of the LH-treated hypophysectomized group decreased more than that of the hypophysectomized control, indicating that LH induced the evacuation of mature spermatozoa from the testes of LH-treated hypophysectomized newts. In the FSH-treated newts, the testicular weight was greater than that in the hypophysectomized control, and was maintained at a value similar to that of the intact control. In the 8 degrees C group, there was no significant difference in testicular size among the intact control, hypophysectomized control, and FSH-treated newts. LH strongly induced spermiation as it did at 18 degrees C. The plasma testosterone level in the hypophysectomized newts decreased dramatically, but LH was effective in restoring it. Its effect was more potent at 8 degrees C than at 18 degrees C. On the other hand, FSH did not induce a significant increase in the plasma testosterone levels at either temperatures. The results indicate a temperature-dependent difference in responsiveness of the testis both in vitro and in vivo to LH and FSH.     

Pituitary regulation of Leydig cell function in the adult male rat.

The effects of hypophysectomy on serum testosterone, 125I-labelled hCG binding to testicular membranes and on testicular responsiveness were studied in adult rats. Serum testosterone decreased rapidly over the first 6 h after hypophysectomy. LH receptors were determined (pmol/testis) by measuring the specific binding of 125I-labelled hCG in membrane preparations of testes of rats hypophysectomized 1, 2, 3, 6, 9, or 15 days earlier. Hypophysectomy did not result in a decrease in 125I-labelled hCG binding on day 1 but this had decreased to 40% of that in intact controls by day 2. A gradual decline was found between days 2 and 6 at which time hCG binding had decreased to 15%. No further decrease occurred between days 6 and 15. Scatchard analysis indicated that the decline in hCG binding was due to a decreaffinity. FSH, testosterone, dihydrotestosterone, and oestradiol were unable to prevent the decline in hCG binding. Although serum testosterone, testicular testosterone content, and 125I-labelled hCG binding decreased rapidly after hypophysectomy, testicular responsiveness to LH was biphasic. The intraperitoneal administration of 25 microgram LH 2 h before decapitation increased testosterone in the circulation to a greater extent extent in animals hypophysectomized for 1 day than in intact controls while hCG binding affinities and capacities had not changed. Two or three days after hypophysectomy testicular responsiveness to LH was similar to that of intact controls even though hCG binding in hypophysectomized animals had decreased to 40 and 28% of intact controls respectively. It is concluded that (1) the testis is dependent on anterior pituitary hormones for maintenance of testicular LH receptors and testosterone secretion, (2) FSH, testosterone, dihydrotestosterone, or oestradiol cannot prevent the decline in testicular LH receptors resulting from hypophysectomy, and (3) steroidogenic capacity of the testis persists significantly longer than the hCG binding capacity of the testis.     

Effects of androgens on the testes of intact and hypophysectomized Japanese quail

The effects of testosterone propionate administered via Silastic capsules on avian spermatogenesis were investigated in intact and hypophysectomized quail with the following results. (1) In intact sexually mature quail low doses of testosterone inhibited luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion and led to testicular regression. Large doses also blocked gonadotrophin secretion but maintained the testes in a spermatogenetically active condition. Testis size was decreased but not seminiferous tubule diameter. A combination of testosterone plus ovine LH or FSH was more effective in maintaining testicular weight. (2) Following complete hypophysectomy of mature quail large doses of androgens were unable to maintain spermatogenesis. Treatment of hypophysectomized birds for 14 days only retarded the rate of testicular regression. (3) Testosterone induced slight testicular growth in intact sexually immature quail maintained on short daylengths, but this spermatokinetic action was lost if the birds were hypophysectomized prior to treatment. (4) In immature quail which were hypophysectomized and treated with testosterone, testosterone plus ovine FSH, or testosterone plus ovine LH, 1 week later, testicular growth was greatest with the testosterone/FSH combination. The data are consistent with the view that androgens play an important role in avian spermatogenesis, as they do in mammals. However, pituitary factors, probably FSH, are also essential for full spermatogenesis and testicular growth to occur.     

Regulation of testicular inhibin subunit messenger ribonucleic acid levels in vivo: effects of hypophysectomy and selective follicle-stimulating hormone replacement

To examine the pretranslational regulation of inhibin subunits in the rat testis by FSH, we studied the effects of hypophysectomy with or without selective FSH replacement on testicular inhibin subunit mRNA levels in immature and adult animals. In the first experiment (Exp I), sexually immature (20-23 days old) intact and hypophysectomized male rats were killed 1, 3, and 7 days after surgery, and the testicular content of inhibin subunit mRNAs was determined by filter hybridization. A second group of immature, intact, or hypophysectomized rats was treated with saline or FSH for 7 days as follows: I) intact, saline; II) hypophysectomized, saline; III) hypophysectomized, FSH [0.05 microgram/100 g BW, sc, twice daily (BID)]; IV) hypophysectomized, FSH (0.50 microgram/100 g BW, sc, BID); V) hypophysectomized, FSH (5.0 micrograms/100 g BW, sc, BID); and VI) hypophysectomized, FSH (50.0 micrograms/100 g BW, sc, BID). In the second experiment (Exp II), adult (60 days old) intact or hypophysectomized animals were treated with saline, FSH, and/or testosterone for 7 days as follows: I) intact, saline; II) hypophysectomized; saline; III) hypophysectomized, 22-mm testosterone implant; IV) hypophysectomized, FSH (50.0 micrograms/100 g BW, sc, BID; and V) hypophysectomized, 22-mm testosterone implant plus FSH (50.0 micrograms/100 g BW, sc, BID. The effects of FSH and testosterone on testicular inhibin subunit mRNA levels were measured by filter hybridization. In Exp I, the level of inhibin alpha-subunit mRNA per testis was significantly lower in hypophysectomized rats than in intact controls at all time points after surgery. Replacement of FSH to hypophysectomized immature rats led to a dose-dependent increase in alpha-subunit mRNA per testis. However, hypophysectomy and FSH replacement had no significant effect on beta-B-subunit mRNA. In adult rats (Exp II), hypophysectomy significantly lowered and FSH replacement increased testicular inhibin alpha-subunit mRNA levels. Replacement of testosterone to adult animals, either alone or in combination with FSH, had no effect on expression of inhibin alpha-subunit mRNA. beta-B mRNA levels in adult testis were not significantly altered by any of the treatments. beta-A-Subunit mRNA levels were below the detection threshold of filter hybridization in both Exp I and II. Collectively, these data demonstrate that FSH regulates alpha- but not beta-B-subunit mRNA in the testis of both immature and adult rats in vivo. Differential regulation of inhibin subunits may provide a mechanism for creation and regulation of functional diversity of inhibin-related peptides in the testis.     

Increase in DNA polymerase alpha activity associated with DNA synthesis due to FSH or oestrogen in ovaries of immature rats

DNA polymerase activities and DNA content of ovaries from immature intact rats (4-29 days after birth), hypophysectomized rats and hormone-treated hypophysectomized rats were measured. During normal ovarian growth DNA polymerase alpha activity and DNA content of ovaries increased. The polymerase activity decreased gradually after hypophysectomy without any alteration in the DNA content. Administration of ovine FSH (2 micrograms/day) or oestradiol-17 beta (1 mg/day) to hypophysectomized rats enhanced ovarian DNA content and DNA polymerase alpha activity, whereas DNA polymerase beta activity did not change significantly. These results suggest that DNA polymerase alpha participates in DNA synthesis in these ovaries. The specific activity of DNA polymerase alpha (the activity per microgram DNA) in the ovaries increased between 4 and 14 days after birth, and then remained almost constant; the specific activity declined gradually after hypophysectomy. Administration of FSH or oestradiol-17 beta but not of ovine LH, progesterone or testosterone to hypophysectomized rats restored the specific activity. Mixing experiments with different kinds of ovarian extracts suggested that no activators of DNA polymerase alpha were present in the extracts. These results suggest that FSH or oestrogen causes the induction of DNA polymerase alpha accompanied by DNA synthesis during cell proliferation in ovaries of immature rats.     

The role of luteinizing hormone in regulation of testicular inhibin alpha and beta-B subunit messenger RNAs in immature and adult animals

In vivo and in vitro evidence indicates that FSH is a primary regulator of testicular inhibin production. However, recent reports suggest that LH may also promote inhibin secretion in vivo. To investigate whether LH regulates inhibin subunit messenger RNA (mRNA) expression as well, we examined the effects of hypophysectomy and LH replacement on the testicular content of inhibin alpha and beta-B subunit mRNAs in sexually immature and adult rats. Twenty- and 60-day-old intact and hypophysectomized rats received saline or 0.25, 2.5, 25.0, or 250 micrograms ovine LH/100 g body wt sc, twice daily for 7 days beginning on the day after hypophysectomy (n = 5/group in three separate experiments). The inhibin subunit mRNA content of each testis was measured for statistical analysis by dot-blot hybridization, and experimental results were confirmed by northern analysis of poly(A) RNA from each sample. In immature animals, the testicular content of both inhibin subunit mRNAs was decreased after hypophysectomy; inhibin alpha and beta-B mRNA levels were decreased to 6.9 +/- 0.9% and 31.7 +/- 2.7% of intact control values, respectively. In adult animals, hypophysectomy resulted in a more modest decrease in inhibin alpha subunit mRNA per testis (44.9 +/- 3.1% of controls) but had no effect on beta-B subunit mRNA. Replacement of LH to immature hypophysectomized animals did not alter levels of mRNA for either inhibin subunit. However, in adults LH restored testicular inhibin alpha subunit mRNA content in testes of hypophysectomized animals to levels seen in intact, saline-treated control animals. LH replacement also slightly but consistently decreased testicular beta-B subunit mRNA content compared to levels seen in hypophysectomized, saline-treated rats. These results indicate that although the response of inhibin subunit mRNAs to pituitary input decreases as a function of sexual maturation, LH may play an important role in regulation of inhibin subunit mRNA expression in adult but not immature testes. The mechanism(s) of LH action on testicular inhibin subunit gene expression is currently unknown, but may involve either direct actions of LH on Leydig cell inhibin subunit mRNAs or indirect actions of interstitial cell factors on Sertoli cell inhibin subunit gene expression.     

Seasonal cycles in gonadal activity and plasma gonadotropin in the musk turtle, Sternotherus odoratus

Plasma gonadotropin cycles were examined in relation to the seasonal gonadal cycle in freshly captured musk turtles, Sternotherus odoratus, from South Carolina. Acute and chronic stress effects of captivity on testicular growth and circulating plasma testosterone (T) and follicle-stimulating hormone (FSH) also were examined. Monthly mean FSH levels in freshly captured males were correlated significantly with plasma T. Both T and FSH were minimal in spring when testes were small, and highest in the fall in males that had begun spermiation and whose testes had begun to regress. Individual plasma T and FSH values were significantly correlated during the fall when both hormones were at elevated levels. In contrast, plasma luteinizing hormone (LH) remained undetectable throughout the year in males. Females had nondetectable levels of both plasma LH and FSH throughout the year. There was a seasonal pattern in plasma 17 beta-estradiol which was correlated with follicular growth. Holding males in captivity (outdoors) reduced plasma T by 35-60% within 24 hr of capture (depending on season) and plasma T remained at these lower levels after 2 weeks. However, FSH was not significantly affected by such short-term "stress." Testicular weight and FSH cycles of captive males were similar to those of males in the field. Monthly plasma T of long-term captives also exhibited a seasonal cycle but at a level significantly lower than in the field and with a delayed peak. Thus, while the data suggest that FSH may be important to both seasonal testicular growth and androgen secretion, fluctuations in FSH alone cannot account for all observed patterns or changes in spermatogenesis or plasma androgen levels.     

Structural manifestations of the rat Sertoli cell to hypophysectomy: a correlative morphometric and endocrine study.

Although the Sertoli cell is a key cell mediating the actions of FSH- and LH-stimulated testosterone (T) in the testis, there is little information to indicate how this cell responds structurally to hormonal insufficiency. The present study used morphometric techniques to study the structural manifestations of the Sertoli cell in adult rats hypophysectomized for 6 and 28 days. Six days posthypophysectomy, a period when germ cell degeneration is first evident, tubular diameter and length, testis weights, volume of the interstitium, and volume of most parameters that comprise the interstitium (except blood vessels) showed significant regressive features. However, virtually no parameter relating to the volume and surface area of the Sertoli cell or its subcellular components was significantly reduced compared with that in the normal animal. Thus, at a time when germ cell degeneration is seen in the testis, the Sertoli cell showed no significant structural response to the changing endocrine status of the animal. In contrast, 28 days after hypophysectomy, virtually all parameters relating to the Sertoli cell and its organelles were significantly decreased compared with those in normal animals. Plasma and tissue testosterone, PRL, and FSH showed a very significant decrease 6 days after hypophysectomy compared with intact animals, but at 28 days there was no further significant decrease in the levels of these hormones. There was no correlation of most organelle volumes and surface areas with endocrine parameters. The size of the Sertoli cell showed positive and significant correlations with the volumes and surface areas of all of its cytoplasmic organelles, except the lipid volume. Short term hypophysectomy resulted in no significant change in either the concentration (femtomoles per mg protein) or the content (femtomoles per testis) of FSH receptors, nor was there a significant change in the number of FSH receptors per cell. However, 28 days after hypophysectomy only the content, not the concentration, of FSH receptors decreased significantly along with a decrease in the number of FSH receptors per cell. Although the marked degenerative changes that are seen in the testis 6 days after hypophysectomy parallel endocrine decline, the Sertoli cell responded slowly from a structural standpoint compared with the Leydig cell. After long term hypophysectomy, significant morphometric changes were observed in all of its structural parameters.     

The endocrine control by luteinizing hormone of testosterone secretion from the testis of the Japanese quail

Injections of chicken or ovine luteinizing hormone (LH) into sexually mature male Japanese quail greatly increased plasma levels of testosterone. Maximal responses were obtained within 15 min of an iv injection and between 1 and 2 hr following sc or im injections. Saline treatment had no effect on plasma testosterone. In chronically castrated quail LH was not effective in altering androgen levels. The responses to LH were dose related, significant increases being obtained following sc injections of 5 μg of chicken LH (fraction AE1) or 10 μg of ovine LH (NIH-LH-S19). Chicken LH (AE1) was appropriately 1.8 times as potent as NIH-LH-S19. Ovine FSH (NIH-FSH-S10) stimulated testosterone release in very large doses (1 mg) but was at least 100 times less active than LH-S19. An iv injection of an antiserum raised against chicken LH into mature male quail caused a rapid decrease in plasma testosterone levels. Treatment with FSH-S-10 for up to 1 week failed to facilitate the subsequent response to an injection of LH. The responsiveness of the testis to exogenous LH was tested at various times during a photoinduced gonadal growth cycle. Sexually immature quail showed only a marginal response to an sc injection of 20 μg of NIH-LH-S19. A marked increase in responsiveness occurred after 6 long days. This coincides with the time when plasma testosterone levels increase naturally after transfer to long daylengths and with the period when Leydig cell maturation becomes complete. These in vivo results add further weight to the belief that, in birds, or at least in the quail, peripheral androgens are controlled by pituitary LH and that FSH plays no significant role in the acute release of testosterone from the mature testis.     

Effects of gonadectomy and steroid treatment on plasma gonadotropins and the response of superfused pituitaries to gonadotropin-releasing hormone in the turtle Sternotherus odoratus

Gonadectomized (gonadex) turtles, Sternotherus odoratus, had significantly elevated plasma FSH, but LH was less consistently affected. Estradiol (E2)-implants suppressed plasma FSH in gonadex females but not in males: testosterone (T) partially suppressed FSH in males. In contrast, E2-treatment markedly suppressed pituitary LH content and in vitro LH secretion in gonadex and intact turtles (inhibitory effects of E2 were less in intact than ovariectomized females). These steroid effects were relatively specific for gonadotropin; pituitary TSH content was not altered. In vitro, pituitary LH secretion responded to doses of GnRH greater than or equal to 1 ng/ml and LH output remained elevated for at least 3 hr of continuous superfusion with gonadotropin-releasing hormone (GnRH). In general, gonadectomy elevated pituitary responsiveness to GnRH while E2 and T suppressed this responsiveness; the effects of E2 are greater in gonadectomized than intact turtles. Thus, negative gonadal feedback appears to be involved in the secretion of gonadotropins in turtles, and steroidal actions may be partly due to suppression of pituitary hormone content and responsiveness to GnRH.     

Serum gonadotropins and steroids associated with breeding activities in the green sea turtle Chelonia mydas. I. Captive animals.

Circulating levels of gonadotropins (FSH and LH) and several sex steroids were studied in a captive colony of green sea turtles, Chelonia mydas, in association with the annual reproductive cycles in 3 years. Limited data for prebreeding and copulating males indicated that gonadotropins remained low and that androgen levels were lower during copulation than in the prebreeding seson. Females showed consistent hormonal profiles from year to year. All steroids were reatively low and increased gradually between the prebreeding and mating season. Estrogen dropped while testosterone peaked in the season of maximal sexual receptivity and both steroids then remained relatively low througout the remainder of the nesting season. In contrast, progesterone (PRO) continued to rise progressively during the prebreeding and mating season and up to the time of nesting. Both gonadotropins were low during the prebreeding season, but only LH rose during the mating season. FSH showed a pronounced but relatively brief “surge” at the time of nesting (oviposition), while LH and PRO were only slightly elevated and variable at this time. FSH levels fell rapidly (with a half-life of 12–21 min) immediately after the completion of laying and remained at baseline levels until the next nesting (in about 11 days). In contrast, simultaneous surges in LH and PRO began between 6 and 12 hr after nesting and lasted for about 24 hr; these hormones then returned to low baseline levels until the next nesting-ovulatory cycle. These internesting peaks in LH and PRO, which were also occasionally observed in mating animals shortly before the start of nesting, were highly correlated with the timing of ovulation. These data are compared with information on the hormonal profiles of the avian ovulatory cycle and seasonal breeding cycles of other turtles. The implications of the relationships among endogenous hormones in the green turtle are discussed in relation to the hypothalamic control of the pituitary and the physiological actions of the gonadotropins and steroids. In particular, data suggest that the secretion of FSH and LH may be regulated independently; and, contrary to existing physiological data, these two gonadotropins may have distinctive roles in ovarian regulation that differ from those suggested by hormone therapy studies.     

Hormonal regulation of deoxyribonucleic acid polymerase beta activity in rat testis

The content of DNA polymerase beta in whole rat testes drastically decreased upon hypophysectomy: at 1 and 2 weeks, to 12.5% and 5% of the control testes of sham-operated rats, respectively. DNA polymerase beta activity per cell (per milligram DNA) also decreased to 14% of the control within 2 weeks after hypophysectomy. The DNA polymerase alpha in the testis also decreased, but the DNA polymerase gamma was relatively resistant to hypophysectomy. The testicular DNA polymerase beta from hypophysectomized rats sedimented at 4.5 S, whereas that from sham-operated controls sedimented at 3.3 S. The reduced level of testicular DNA polymerase beta and the change in molecular size induced by hypophysectomy were largely reversed by daily injections of LH and FSH. The reduced activity was also fully reversed by the injection of testosterone. These results suggest that the level of DNA polymerase beta in the rat testis depends largely on the level of testosterone produced by Leydig cells in the testis itself, but is also regulated by pituitary gonadotropins.     

Effect of neuraminidase treatment on the biological activity of highly purified ovine FSH and LH in hypophysectomized immature male and female rats.

Highly purified ovine FSH and LH were treated with neuraminidase to remove sialic acid and the desialylated derivatives were examined for biological activity in hypophysectomized immature male and female rats. The male rats were hypophysectomized at 22 days of age and beginning on day 25 were injected sc twice daily for 4 days with native or neuraminidase-treated FSH (total dose, 15 or 60 mug) or LH (12 mug). The ventral prostates, seminal vesicles, and testes were then removed and weighed, and serum testosterone levels were measured by radioimmunoassay. The female rats were hypophysectomized on day 28 and beginning on day 35 were injected sc twice daily for 4 days with native or neuraminidase-treated FSH (8 mug) or saline. On the morning of day 39, the rats were given an ovulating dose of gonadotropin (8 mug native or neuraminidase-treated FSH, or 1.28 mug native or neuraminidase-treated LH) or 1.0 ml saline iv via tail vein. Twenty-four hours later ova were counted in the oviducts the ovaries were weighed, and serum levels of progesterone and 20alpha-dihydroprogesterone were determined by radioimmunoassay. Treatment of ovine LH with neuraminidase did not diminish the ability of this hormone to increase prostate and testes weights and serum testosterone levels. Desialylation also did not decrease the ability of LH to induce ovulation. Although native ovine FSH significantly increased the weights of the ventral prostate, seminal vesicles, and testes, and elevated plasma testosterone levels, the desialylated derivative was essentially inactive. Neuraminidase treatment also eliminated the ability of ovine FSH to increase ovarian weight, to induce ovulation, and to elevate serum progesterone and 20alpha-dihydroprogesterone. These results indicate that the LH-like activity of ovine FSH is an intrinsic property of the FSH molecule.     

Plasma testosterone levels in male turtles, Chrysemys picta, following single injections of mammalian, avian and teleostean gonadotropins.

The response of male turles (Chrysemys picta) to single injections of either mammalian (human, ovine), avian (domestic hen) or teleostean (salmon) gonadotropins was studied at different points of the testicular cycle (May, July, November) by measurement of plasma testosterone. Mammalian FSH's and avian FSH and LH were markedly stimulatory, and the responses were qualitatively and quantitatively similar. Further, the condition of the testis at the time of injection did not appear to affect the response, with the exception that it was quantitatively less in May. The response was characterized by: (a) Rapidity, reaching maximum or near maximum between 1 and 2 hr postinjection. (b) Magnitude, rising from 10 to 20 ng T/100 ml plasma to 1200 ng/100 ml plasma. (c) Duration, not returning to original plasma levels of T until between 96 and 192 hr postinjection. Injections of purified ovine and human FSH at levels calculated to be equivalent in hormone content to 50 μg of ovine FSH standard duplicated the response. The response was dose related, a 50 μg dose of ovine FSH evoking a response about 10-fold that of a 5 μg injection. Injections of up to 50 μg of NIH ovine LH standard, or 25 μg purified ovine LH only doubled plasma T levels and 100 μg of teleostean gonadotropin had no effect.