Detection of hormone release from individual cells in mixed populations using a reverse hemolytic plaque assay

Prolactin (Prl) secreting cells in a mixed pituitary cell culture form microscopically-identifiable plaques (zones of hemolysis around the lactotropes) when incubated in a monolayer with staphylococcal protein-A-coated ovine erythrocytes in the presence of Prl antiserum and complement. Plaques form first at 15-30 min and are maximal in size and number at 2 h. Approximately 70% of the adenohypophyseal cells form plaques under these conditions. TRH increases, and dopamine decreases, the size and number of plaques at early times during incubation. This reverse hemolytic plaque assay probably can be used to detect any cell secretion for which an antibody is available. This technique, or a modified version of it in which sequential plaque assays are performed on identified cells--used together with immunocytochemistry, autoradiography or electron microscopy of those cells--should provide better answers to commonly asked questions about secretory systems: Do all or only a subset of cells containing the same hormone respond to a particular secretagogue? Can cells that contain two hormones release one of them preferentially?     

Capacity of individual somatotropes to release growth hormone varies according to sex: analysis by reverse hemolytic plaque assay

A reverse hemolytic plaque assay was used to investigate the mechanism(s) underlying sexual differences in GH release which evolve at puberty in rats. The percentages of GH-secreting cells in 24-h pituitary cultures from each sex were similar for pituitary donors up to 30 days of age (range = 38.9% to 41.7% of all cells in culture, n = 3 separate experiments) but decreased by day 50. The decrease was more striking for females (to 24.1 +/- 0.3% mean +/- SE) than for males (to 33.2 +/- 1.1%). However, owing to the greater increase in total pituitary cell number exhibited by female rats at this time, the absolute numbers of somatotropes recovered from male and female pituitaries were almost identical on 50 and 100 days of age. To assess the secretory capacities of individual somatotropes, we measured the sizes of plaques formed. In prepubertal rats (days 10-30), the plaque areas under basal conditions were comparable for males and females at each age studied, and treatment with GH-releasing factor increased plaque sizes to approximately the same degree (10-fold) for both sexes at each age. However, by day 100, plaques that formed under both basal and stimulated conditions were consistently larger (P less than 0.01) for male than for female donors. Taken together, our results demonstrate that sexual differences in GH release are attributable to the secretory capacities of individual somatotropes rather than to differences in the numbers of GH cells in pituitaries of male and female rats.     

The somatostatin analog SMS 201-995 induces long-acting inhibition of growth hormone secretion without rebound hypersecretion in acromegalic patients

The acute effect of the somatostatin analog SMS 201-995 (SMS) was investigated in eight acromegalic patients. This substance is an octapeptide [DPhe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr-(ol)] that inhibits GH release in experimental animals and man. After a control day, 50 micrograms SMS were injected sc, and plasma GH and insulin and blood glucose levels were measured at multiple intervals for 24 h. GH significantly (P less than 0.001) decreased in seven of eight acromegalic patients from 30 +/- 5 (+/- SE) to an average of 10.7 +/- 4 micrograms/l from 1-10 h after drug administration. No rebound effect occurred. Postprandial blood glucose levels were significantly (P less than 0.01) higher between 2 and 4 h after SMS treatment compared with control day values, and there was a substantial reduction in insulin secretion, as estimated by the area under the curve (P less than 0.01), during the first 3 h after SMS administration. Circulating GH was not altered by SMS or the dopamine agonist mesulergine in one patient, but the combination of both substances (50 micrograms SMS, sc, and 0.5 mg mesulergine, orally) reduced GH to below 50% of basal. In vitro studies showed that 1 PM, 0.1 nM, and 10 nM SMS or natural somatostatin exerted a similar inhibitory effect (12-39% reduction; P less than 0.01 for all three strengths) on GH release by cultured human pituitary tumor cells. In conclusion, the somatostatin derivative SMS exerts a potent and prolonged inhibitory action on GH secretion and a shorter lasting suppression of insulin in acromegalic patients. Therefore, it may represent a useful tool in the chronic management of this condition.     

Does SMS 201-995 normalize growth hormone secretion in acromegaly? GH day profiles and GH concentrations after oral glucose loading

GH secretion in acromegaly was studied in 8 patients before and during treatment with SMS 201-995, a somatostatin analogue, 100 micrograms twice daily, by evaluating GH day profiles and GH suppressibility after oral glucose tolerance tests (OGTT). Normalization of GH secretion, estimated by OGTT, was only observed in the three patients who had a decrease in plasma GH to less than 2 micrograms/l after SMS 201-995 injection, and who had the lowest mean plasma GH levels during the day and the largest percent decline of mean plasma GH levels. We conclude that real normalization of GH secretion during SMS 201-995 therapy only occurs in a subset of patients. The data illustrate that the applicability of the generally held cut-off value of 5 micrograms/l, between normal and abnormal plasma GH, has to be reconsidered in the case of chronic intermittent subcutaneous therapy with SMS 201-995.     

Detection of LH release from individual pituitary cells by the reverse hemolytic plaque assay: estrogen increases the fraction of gonadotropes responding to GnRH

Gonadotropes that secrete LH were demonstrated microscopically among mixed anterior pituitary (AP) cells in culture with a reverse hemolytic plaque assay. LH released from a cell binds to adjacent RBCs bearing an LH Ab-protein A complex which results in a zone of complement-mediated hemolysis (a plaque) surrounding each gonadotrope. In untreated cultures a few, small plaques formed, but in the presence of hypothalamic GnRH (10(-7) M, a maximally stimulating dose) a 10-fold increase occurred in their number and size. Non-secretory gonadotropes were found in the pituitary of diestrous animals: 5-6% of all AP cells contained immunocytochemically detectable LH whereas only 2.5-3.0% formed plaques in the presence of GnRH (10(-7) M). Nearly all of the gonadotropes were secretory at proestrus. Estradiol treatment of diestrous cultures for 24 h increased the fraction of secretory gonadotropes to near the level observed in proestrous cultures. These results demonstrate the utility of the reverse hemolytic plaque assay for detection of LH secretion from individual gonadotropes, establish that not all cells containing LH can secrete it, and suggest that a previously unrecognized mode of estrogen action to evoke the preovulatory LH surge is mediated by increasing the fraction of secretory gonadotropes.     

Analysis of hormone secretion by clinically nonfunctioning human pituitary adenomas using the reverse hemolytic plaque assay

The reverse hemolytic plaque assay was used to study hormone release in vitro by seven clinically nonfunctioning human pituitary adenomas associated with no clinical or biochemical evidence of hormone excess. Four of seven tumors were oncocytomas, one a null cell adenoma, and two gonadotroph adenomas based on immunocytochemical and ultrastructural features. In all seven tumors, plaques were formed with antiserum against beta FSH; four produced plaques for beta LH, and five for glycoprotein hormone alpha-subunit. The percentage of plaque-forming cells and the mean size of plaques were smaller than those of clinically functioning adenomas studied for comparison (five GH- and/or PRL-producing adenomas). These results correlated with those of hormone release in tissue culture, immunocytochemistry on paraffin secretions of the tumors, and immunocytochemistry after reverse hemolytic plaque assay. We conclude that clinically nonfunctioning pituitary adenomas release small quantities of hormones, primarily gonadotropins, and that hormone release is attributable to only a small percentage of tumor cells.     

A cellular basis for growth hormone deficiency in the dwarf rat: analysis of growth hormone and prolactin release by reverse hemolytic plaque assay

The purpose of this study was to elucidate the cellular basis for growth hormone deficiency in Lewis-derived dwarf rats. To this end, we used reverse hemolytic plaque assays to evaluate hormone release. This allowed us to determine the proportional abundance of GH- and PRL- secreting cells and estimate the relative amount of hormone secreted by individual pituitary cells from dwarf rats and their somatically normal counterparts. The percentage of all pituitary cells that released GH (formed plaques) in pituitary dispersions was substantially lower for dwarfs when compared with normals in the absence (3.8 +/- 2.2% vs. 43.4 +/- 2.2%) or presence (6.6 +/- 3.8% vs. 45.7 +/- 1.4%; n = 3) of GRF. In addition, GH secretors from dwarfs released less hormone (formed smaller plaques) than their normal counterparts under both basal and stimulated conditions. An analysis of the relative number of GH cells that formed plaques of various sizes was accomplished by constructing a frequency distribution. Dwarf GH secretors formed more small plaques and proportionately fewer larger plaques than normals under both basal and stimulated conditions. For comparison, we also quantified the proportions of PRL secretors and found that they were actually more abundant in dwarfs than normals in the absence (52.4 +/- 4.6% vs. 33.7 +/- 3.7%) or presence (53.4 +/- 4.9% vs. 33.8 +/- 4.1%; n = 4) of TRH. Treatment with this secretagogue consistently increased mean PRL-plaque area for both groups. Our findings demonstrate that dwarf rats are severely deficient in the proportion of GH secretors. In addition, the few GH secretors present in the dwarf pituitary were less responsive to GRF than normals. In contrast, PRL cells in dwarfs appear to be functionally similar to those of their normal counterparts. The reciprocal relationship in the proportions of GH and PRL secretors in dwarfs provides a rather unique model for investigating the functional relationship between these cell types.     

Long term treatment with the somatostatin analog SMS 201-995 in a patient with a thyrotropin- and growth hormone-secreting pituitary adenoma

A patient with a mixed pituitary tumor secreting TSH and GH was treated, starting 3 months after partial adenomectomy, with the somatostatin analog SMS 201-995 for 8 months. Somatostatin itself inhibited TSH, GH, and alpha-subunit release by the tumor both in vivo and in vitro. Long term treatment with twice daily sc injections of SMS 201-995 resulted in decreased TSH secretion and lower serum thyroid hormone levels. However, euthyroidism was achieved only when the patient was treated with three daily 200-micrograms injections of SMS 201-995. After 30 weeks of SMS 201-995 therapy, TSH secretion increased, while GH secretion remained suppressed. After withdrawal for 6 months, SMS 201-995 (100 micrograms, sc, twice daily) again completely inhibited TSH secretion. SMS 201-995 did not alter the volume of the residual adenomatous tissue. We conclude that SMS 201-995 may be a valuable therapeutic agent for the management of patients with a thyrotroph adenoma. However, desensitization may occur during long term treatment.     

SMS 201-995 induces a continuous decline in circulating growth hormone and somatomedin-C levels during therapy of acromegalic patients for over two years

Ten acromegalic patients, four previously untreated, were studied before and at regular intervals during treatment with the long-acting somatostatin analog SMS 201-995 (200-300 micrograms daily for 2 or 3 sc injections for 16-108 weeks). All patients had rapid clinical improvement, with disappearance of excessive perspiration, paresthesias, and headache within the first 6 weeks of therapy. The mean 24-h serum GH concentrations fell from 44.0 +/- 7.8 (+/-SE) micrograms/L before to 5.9 +/- 1.0 microgram/L at the end of therapy. The GH levels from 2-6 h after the acute administration of 50 micrograms SMS 201-995 before the start of therapy correlated significantly with the mean 24-h GH concentrations after 16-108 weeks of treatment (P less than 0.05). The initially increased serum somatomedin-C (Sm-C) levels normalized in 5 of these 10 patients; the mean values were 7.3 +/- 0.9 U/mL before and 2.9 +/- 0.7 U/mL at the end of therapy. The Sm-C and mean GH levels continuously decreased during long term therapy; the concentrations after 1.5-2 yr of therapy were significantly lower than those after 6-12 months of therapy (P less than 0.01 and P less than 0.01, respectively). A slight decrease in the size of the pituitary tumor was noted by computed tomography in three of six patients. Transient clinically detectable steatorrhea occurred in two patients. Postprandial hyperglycemia occurred during therapy in eight patients, while in two patients with type 2 diabetes mellitus carbohydrate tolerance improved in one and deteriorated in the other. SMS 201-995 is a highly effective medical treatment for acromegaly. Clinically improvement occurs rapidly, and the inhibition of serum GH and Sm-C levels persisted even after more than 1 yr of therapy. No important subjective side-effects were noted. SMS 201-995 is an excellent drug in patients in whom acromegaly persists after surgery and for interim treatment to shorten the period of clinical activity after irradiation.     

Different responses of growth hormone secretion to guanfacine, bromocriptine, and thyrotropin-releasing hormone in acromegalic patients with pure growth hormone (GH)-containing and mixed GH/prolactin-containing pituitary adenomas

There is great variability in the GH secretory responses to different stimuli in patients with acromegaly. In the present study, we compared the effects on GH secretion of two compounds (bromocriptine and TRH), which presumably act directly at the pituitary level, with the effect of the centrally acting alpha-adrenergic agonist guanfacine in 14 untreated acromegalic patients. These in vivo responses of GH release were correlated with the results of immunocytochemical studies of the pituitary adenomas. In nine patients with pure GH-containing adenomas, GH secretion was suppressed by bromocriptine by more than 50% in one patient, while TRH stimulated GH release by more than 100% in another patient. Guanfacine (2 mg, orally) did not elicit a change in circulating GH levels in any of these nine patients. In the group of five patients with mixed GH/PRL-containing adenomas, however, bromocriptine suppressed GH levels by more than 50% in all patients, and TRH stimulated GH release by more than 100% in four of them. Guanfacine stimulated GH secretion significantly in four of these five patients. Guanfacine inhibited GH secretion significantly in five other acromegalic patients who had been treated 5-10 yr previously by external pituitary irradiation. We conclude that in acromegaly, the presence of PRL within the GH-secreting pituitary adenoma makes GH secretion more sensitive to bromocriptine and TRH, while normal sensitivity to hypothalamus-mediated stimulation (alpha-adrenergic agonist) is retained to some extent. In contrast, pure GH-secreting tumors responded little or not at all to bromocriptine, TRH, or guanfacine.     

Pituitary adenylate cyclase activating polypeptide, growth hormone (GH)-releasing peptide and GH-releasing hormone stimulate GH release through distinct pituitary receptors.

GH secretion has been thought traditionally to be regulated by the two hypothalamic hormones, GH-releasing hormone (GHRH) and somatostatin (SRIF). Recent evidence has suggested that other factors may be involved. These factors include the natural ligand for the synthetic hexapeptide GH-releasing peptide (GHRP) and the putative hypophysiotropic factor pituitary adenylate cyclase-activating polypeptide (PA-CAP). Accordingly, we examined the effects of GHRP and PACAP on GH secretion at the single cell level using the reverse hemolytic plaque assay which allows distinction of effects on the number of secreting cells and the amount of hormone each cell secretes. Both factors stimulated GH secretion in a dose-dependent fashion, with PACAP being more effective. PACAP increased both the number of cells secreting and the mean amount of hormone secreted per cell. In contrast, GHRP increased the number of secreting cells, although it had no effect on the amount of secretion per cell. GH secretion induced by GHRH, GHRP, and PACAP was inhibited by SRIF, but the effect was predominantly on the number of cells secreting rather than the amount secreted per cell. Specific antagonists to GHRP and GHRH inhibited GH secretion induced by the respective agonist but not that induced by the other factor nor by PACAP. These findings confirm the complex nature of the regulation of GH secretion at the level of the somatotrope. At least three factors, operating via distinct receptors, are able to increase GH secretion. In addition, they ascribe a potential physiological role for the hitherto putative hypophysiotropic factor PACAP.     

Atypical McCune-Albright syndrome associated with growth hormone-prolactin pituitary adenoma: natural history, long-term follow-up, and SMS 201-995--bromocriptine combined treatment results.

A 35-yr-old woman is described as having atypical McCune-Albright syndrome, associated with acromegaly and hyperprolactinemia due to pituitary adenoma. The patient did not present sexual precocity, but primary amenorrhea. After transphenoidal adenomectomy, the GH plasma levels returned to normal, whereas the PRL values decreased; bromocriptine therapy normalized PRL levels and induced ovulatory menses. After 4 uneventful yr the patient developed relapse of active acromegaly that did not recover after a second neurosurgical exploration. Bromocriptine treatment maintained normal PRL levels but did not significantly reduce GH ones; the association with long-acting somatostatin analog SMS 201-995 by continuous sc pump infusion induced definitive control of GH and somatomedin-C secretion. These results suggest an additive inhibitory effect on GH secretion exerted by the two drugs.     

Suppressing actions of butyrate on growth hormone (GH) secretion induced by GH-releasing hormone in rat anterior pituitary cells

We assessed the inhibitory effects of butyrate on the growth hormone (GH) secretion in order to investigate the cellular mechanisms in rat somatotrophs. Isolated anterior pituitary cells were cultured in DMEM for several hours, either in the presence (1, 3, or 10mM) or absence of butyrate, and then stimulated with 10(-7)M GHRH for 30 min, in the presence of butyrate at the concentrations used for the previous culture. The increase in GHRH-induced GH release was significantly reduced in a time-dependent and concentration-dependent manner in the cells previously cultured with butyrate. GH content (the sum of GH released into the medium induced by GHRH stimulation and the GH remaining in the cells after stimulation) was reduced by the culture of cells in the presence of butyrate, which was also inversely dependent on the concentrations used for the culture. Simultaneous addition of an L-type Ca(2+) channel blocker, nifedipine (10 pM), to the medium during 10(-9)M GHRH stimulation significantly reduced the stimulated GH release, which was further significantly decreased by a simultaneous addition of 10 mM butyrate. Butyrate blunted the GHRH (10(-9)M)-induced increase in cellular cyclic AMP and calcium ion concentrations, the activity of protein kinases (A and C), and GHmRNA expression. The expression of mRNA for GPR 41 and 43, known as receptors for short-chain fatty acids, was confirmed in the anterior pituitary cells. These findings suggest that butyrate inhibits GHRH-induced GH release as well as GH production, and the cellular inhibitory actions of butyrate occur in diverse cellular signaling pathways of rat somatotrophs.     

Reduction of pituitary size by the somatostatin analogue SMS 201-995 in a patient with an islet cell tumour secreting growth hormone releasing factor

Acromegaly is rarely caused by the ectopic secretion of growth hormone releasing factor (GRF) from peripheral neuroendocrine tumours. We evaluated the ability of a recently developed somatostatin analogue (SMS 201-995, Sandoz) to reduce hormone levels and pituitary size in a young woman with acromegaly and Zollinger-Ellison syndrome secondary to a metastatic pancreatic islet cell tumour secreting GRF and gastrin. Gastrin, GRF, and growth hormone (GH) levels declined dramatically following the initiation of therapy with the analogue by continuous iv infusion. Although intermittent sc therapy was not effective in suppressing hormone levels, continuous sc infusion of SMS 201-995 has provided good control of both GRF and GH levels for nine months. Moreover, treatment with SMS 201-995 was associated with a substantial reduction in pituitary enlargement and an improvement in her gastric symptoms. Continuous sc infusion of SMS 201-995 may be useful in treating enlarged pituitaries resistant to other modes of therapy.     

Structure-function correlations of growth hormone or/and prolactin-producing pituitary adenomas: an in vitro study with the reverse hemolytic plaque assay

The purpose of this study was to detect in vitro growth hormone (GH) and prolactin (PRL) secretion from adenomas clinically associated with GH or PRL hypersecretion. The reverse hemolytic plaque assay (RHPA) was applied in order to reveal possible differences among various morphologic adenoma types, and to examine the inhibitory effects of octreotide on GH release as well. The 20 surgically resected pituitary adenomas studied included 15 from acromegalic patients and 5 from patients with hyperprolactinemia. All adenomas were diagnosed by histology, immunocytochemistry and electron microscopy. Among tumors associated with acromegaly, 5 were densely granulated (DG), 5 were sparsely granulated (SG) somatotroph (SM) adenomas, 2 were mammosomatotroph (MSM) and 3 mixed somatotroph-lactotroph cell (mixed SM-LT) adenomas; tumors causing hyperprolactinemia included 4 lactotroph (LT) adenomas and 1 mixed SM-LT adenoma. GH release assessed by the RHPA corresponded to in vivo hormone secretion and to tissue immunoreactivity. Statistical analysis showed significant differences among all morphologic types of SM adenomas, exclusive of SG-SM adenomas compared to mixed SM-LT adenomas. The mean plaque size in DG-SM and MSM adenomas was significantly greater than that of SG-SM and mixed SM-LT adenomas, indicating higher GH secretion by the former two types during the same incubation time. PRL secretion was documented in 2 mixed SM-LT adenomas. Plaques for PRL, but not for GH were formed in all LT adenomas. In all SM and LT adenomas, cells producing large plaques represented a minority of the plaque-forming cell population, however, they accounted for the largest part of the total plaque area, thus the largest part of hormone secretion. Octreotide effects on GH release were studied in 6 adenomas by the RHPA. Octreotide treatment induced a rapid and significant reduction in GH secretion by SM cells in vitro, with a selective effect on high-secreting cells.     

Sertoli cells in culture are heterogeneous with respect to transferrin release: analysis by reverse hemolytic plaque assay

It has been reported that not all Sertoli cells store the same product or respond morphologically to secretagogue stimulation. The following studies were performed to determine whether functional differences among these cells are also present with respect to the secretion of a product. Sertoli cells obtained from 18- to 20-day-old rats were cultured for 3 days and then subjected to reverse hemolytic plaque assays for transferrin (TF). Release of TF could be detected from only 62.7 +/- 0.47% (mean +/- SE; n = 4 experiments) of all cells in culture. Results obtained from immunocytochemical staining of different batches of cells from the same dispersions agreed quite closely with these plaque assay values, indicating that not all Sertoli cells in culture contain or secrete TF. Differences in the basal rate of TF release were observed among these secretors, as evidenced by a gradual appearance of plaques over an 8-h period. Addition of FSH, cAMP, or isoproterenol to the assay incubation mixture resulted in an acceleration in the rate of plaque formation. Although approximately twice as many secretors could be identified after 0.5 and 1 h of incubation in the presence of these agents than in their absence, it still required at least 4 h for the remainder of the TF cells to form plaques. This would indicate that only a portion of all TF secretors respond acutely to these modulators. Thus, our observations that not all Sertoli cells secrete TF, and those that do release this substance respond differently to at least three stimulatory agents demonstrate clearly that Sertoli cells are heterogeneous with respect to TF release. Moreover, these findings raise the possibility that differences in the functional capacity of individual cells may be an important factor contributing to the modulation of Sertoli cell secretion.     

Analysis of mammosomatotropic cells in normal and neoplastic human pituitary tissues by the reverse hemolytic plaque assay and immunocytochemistry

The reverse hemolytic plaque assay (RHPA) was used to study hormone release from cultured normal and neoplastic human pituitary cells. The RHPA revealed a lower percentage of GH- and PRL-producing cells in normal and neoplastic pituitaries compared to the percentage of these cells revealed by immunocytochemical (ICC) staining for GH and PRL. Normal pituitary tissues as well as some PRL- or GH-producing adenomas contained large numbers of mammosomatotropic (MS) cells when analyzed by RHPA, combined RHPA-ICC, and ultrastructural immunohistochemistry with immunogold labeling. The percentage of GH and PRL cells in normal pituitaries ranged from 37-51% and 30-60%, respectively, by RHPA, while the percentage of MS cells ranged from 29-49%. The percentage of GH and PRL cells in normal pituitaries estimated by ICC ranged from 53-65% and 32-55%, respectively, while the percentage of MS cells estimated with this technique ranged from 26-50%. Double labeling with the immunogold technique detected GH and PRL in the same cells and within the same granules in both normal and neoplastic pituitary cells. These results indicate that MS cells are present in normal human pituitaries as well as in some pituitary adenomas, and in some pituitaries these two hormones are stored within the same secretory granules.     

In vitro regulation of growth hormone (GH) release from ovine pituitary cells during fetal and neonatal development: effects of GH-releasing factor, somatostatin, and insulin-like growth factor I

Using a monolayer approach, we have examined the acute (3 h) effects of GRF, somatostatin (SRIF), and insulin-like growth factor I (IGF-I) on GH release from pituitary cells of male and female 70-, 100-, and 130-day-old fetuses and newborn lambs and of prepubertal male lambs. GRF stimulated basal GH release in a dose-dependent (10(-12)-10(-8) M) manner at each stage in development. There was no linear relationship between maximal response and increasing age of the donor animals. The ED50 values for GRF were similar in all groups, except in the pituitaries from male and female 130-day-old fetuses, where the ED50 values were significantly higher. SRIF elicited a dose-related (10(-10)-10(-6) M) inhibition of basal GH secretion at each stage of fetal life and in the prepubertal period; although the response was lower in the youngest fetal pituitaries, there was no significant change in maximal response during the fetal or prepubertal period. No effect of SRIF on basal GH secretion was observed in newborn lambs. However, SRIF (10(-7) M) was able to block GRF (10(-8) M)-stimulated GH release in 100- and 130-day-old fetal and prepubertal as well as newborn lamb pituitary cells. Plasma IGF-I concentrations increased from 15.0 +/- 0.7 (mean +/- SE) and 13.8 +/- 0.9 ng/ml for male and female animals, respectively, at 70 days gestation to 55.8 +/- 3.2 and 51.8 +/- 11.1 ng/ml at the time of birth. The increase was much more pronounced in prepubertal lambs, especially in male animals, where IGF-I levels reached 300.8 +/- 37.7 ng/ml. IGF-I (100 ng/ml) had no effect on basal GH release in 70- and 100-day-old fetal, newborn, and prepubertal lamb pituitary cultures, but significantly inhibited basal GH secretion from 130-day-old fetal cells. This dose of IGF-I had no effect on GRF (10(-9) M)-stimulated GH release at 70 days gestation. It significantly inhibited this effect at 100 days and in prepubertal lamb cells. In 130-day-old fetal and newborn lamb pituitary cultures, IGF-I completely blocked the GH response to GRF.(ABSTRACT TRUNCATED AT 400 WORDS)     

Differential effects of somatostatin (SRIH) and a SRIH analog, SMS 201-995, on the secretion of growth hormone and thyroid-stimulating hormone in man

We compared the ability of SRIH and SRIH analog, SMS 201-995 (SMS), to inhibit stimulated GH and TSH secretion in men who received 120-min iv infusions of saline, SRIH (5, 50, and 500 micrograms/h), and SMS (3, 30, and 300 ng/kg.h) together with a bolus iv injection of GHRH (1 microgram/kg) and TRH (500 micrograms). Integrated GH secretion during the 60 min after GHRH plus TRH injection was decreased compared to that after saline by (mean +/- SE) 32 +/- 14% (P = 0.059), 78 +/- 5% (P less than 0.001), and 88 +/- 3% (P less than 0.001) during the 5, 50, and 500 micrograms/h SRIH infusions, and by 13 +/- 7% (P = NS), 50 +/- 15% (P less than 0.05), and 80 +/- 6% (P less than 0.001) during the 3, 30, and 300 ng/kg.h SMS infusions. In contrast, integrated TSH secretion was unaltered during the 5 micrograms/h SRIH and 3 ng/kg.h SMS infusions; it decreased by only 43 +/- 5% (P less than 0.001) and 66 +/- 4% (P less than 0.001) during the 50 and 500 micrograms/h SRIH infusions and by 33 +/- 8% (P less than 0.05) and 50 +/- 3% (P less than 0.001) during the 30 and 300 ng/kg.h SMS infusions. Analysis of the dose-response curves indicated approximately 10- and 5-fold greater potencies of SRIH and SMS, respectively, in inhibiting GH as compared to TSH secretion. These results quantify the effect of SRIH as an inhibitor of GH secretion and suggest that if SRIH has a physiological role in the inhibition of TSH secretion in man, it is limited to conditions associated with marked suppression of GH.