Effects of electrochemical stimulation of medial preoptic area on prolactin and luteinizing hormone release in old female rats

Summary Serum prolactin and LH levels in old constant estrous rats were higher than in old pseudopregnant rats. Electrochemical stimulation of the medial preoptic area in old constant estrous rats resulted in significant increases in serum concentration of prolactin and LH, and subsequent ovulation. Old pseudopregnant rats showed only a small increase in serum prolactin, no increase in serum LH and no ovulation. The high circulating levels of estrogen in old constant estrous rats, and the relative lack of estrogen and the presence of progesterone in the old pseudopregnant rats, may account for the differences observed in response of the medial preoptic area to electrochemical stimulation.Aided in part by NIH research grants CA 10771 and AM 4784.     

Effects of electrochemical stimulation of the hypothalamus on serum prolactin and LH in rats

Summary Plasma levels of prolactin and LH were measured by radioimmunoassay following electrochemical stimulation of the medial preoptic area (MPO) or the arcuate nucleus (Arc.N.) in pentobarbital anesthetized proestrous rats. Differences in the secretion pattern of prolactin and LH were observed when stimulated by means of acutely or chronically implanted electrodes. Acute implantation and stimulation of the MPO resulted in no change in serum prolactin levels, whereas stimulation by means of chronically implanted electrodes evoked a marked increase in serum prolactin. The general observation was that electrostimulation in the acute experiments causes a less sharp but more prolonged prolactin and LH release from pituitary than stimulation through chronically implanted electrodes.Aided in part by NIH research grants CA 10771 and AM 4784.     

Effects of acute stress on the day of proestrus on sexual behavior and ovulation in female rats: participation of the angiotensinergic system

Physical or emotional stress can affect the female reproductive physiology and angiotensin II (Ang II) is a hormone that participates in the stress response and also in the control of reproductive hormones. The present study aimed at evaluating the effects of acute stress in the morning and afternoon of proestrus on sexual behavior and ovulation and the participation of Ang II in the stress-induced effects. Female rats with regular estrous cycles were used. Several different stress protocols were tested in the morning and in the afternoon of proestrus: restraint stress 10 min; restraint stress 1 h and ether stress, respectively. The participation of Ang II was evaluated by injecting Ang II receptor antagonists (losartan and PD123319) 15 min before stress. The lordosis quotient was recorded and the number of oocytes was counted. Plasma levels of luteinizing hormone, progesterone, prolactin and corticosterone were measured. All types of stress in the morning of proestrus induced a reduction in the number of oocytes. Restraint stress (1 h) in the afternoon of proestrus induced a significant reduction in the lordosis quotient. Peripheral and central losartan, but not PD123319, injections partly reverted the effects of stress on ovulation in the morning of proestrus. Acute stress in the morning of proestrus also reduced luteinizing hormone, progesterone and prolactin surges later on the same day. In conclusion, acute stress on the day of proestrus can affect female reproductive physiology. Moreover, the angiotensinergic system, through AT(1) receptors, participates in the effects of acute stress in the morning of proestrus.     

Interactions of oestrogens and hours of sleep on cortisol,FSH, LH,and prolactin in hypogonadal women

The effects of conjugated oestrogens 0.625 mg and placebo on adrenal and pituitary hormones were compared in 10 postmenopausal women during their sleep by means of a double blind prospective crossover study. On placebo, the women had nocturnal variations in LH, prolactin and cortisol concentrations. However, oestrogen administration selectively blunted LH and prolactin changes, but not the rise in cortisol.     

Effects of electroconvulsive shock on food and water intake in the rat

Forty-two male rats were habituated to laboratory conditions for four weeks under constant light conditions. Food and water intakes were recorded daily. Following the habituation period half of the animals were given electroconvulsive shock (ECS) and half Sham-ECS (SECS). ECS treatments produced significant decrements in both food and eater intakes which returned to baseline levels after three days.     

大鼠肝细胞泌乳素受体的研究

本文以~(125)I-oPRL为放射催标记配体,利用受体放射分析法,对哺乳期大鼠肝细胞泌乳素受体进行了研究。结果表明。大鼠肝细胞泌乳素受体与泌乳素的结合具有高度特异性和可饱和性,而且受反应时间和pH值大小的影响;这种结合并非简单的双分子反应,大鼠肝细胞泌乳素受体很可能存在两种亲和力高低不同的结合位点(Kd_1=3.20×10~(10)M,Kd_2=1.26×10~(-8)M)或负协同调节。本研究为将来深入开展泌乳素对肝脏机能调节机制的探讨打下了基础。     

In vivo release of neurotransmitters in the medial basal hypothalamus of the monkey

Summary In vivo release rates of norepinephrine (NE), epinephrine (E), dopamine (DA), gammaaminobutyric acid (GABA), glutamate (GLU) and beta-endorphin (E) in the medial basal hypothalamus (MBH) of unanaesthetized female macaca fascicularis monkey, and the effects thereon of estrogen (E2) treatment, have been estimated using pushpull perfusion methodology. DA, NE, E, GABA, GLU and E were all detectable in 30 min perfusate fractions. No direct correlation between their release rates and those of LH and PRL could be observed. E2 induced an initial decrease, then an increase, in LH and PRL secretion, and concomitant changes in the release patterns of DA, NE, E. GABA and GLU were apparent. This study demonstrates that in vivo push-pull perfusion methodology may be applied to the unanaesthetized monkey, and when combined with venous catheterization for serial blood sampling may prove to be a powerful tool in the investigation of the central molecular events governing neuroendocrine functions.     

The 24 h pattern of pulsatile luteinizing hormone, follicle stimulating hormone and prolactin release during the first 8 weeks of lactational amenorrhoea in breastfeeding women.

In women, breastfeeding results in a variable period of ovarian inactivity which is apparently related to suppression of the normal pulsatile release of luteinizing hormone (LH). However, pulse profiles had only been studied during the daytime. Since resumption of pulsatile LH secretion during puberty is initiated at night, the present study determined the pattern of pulsatile LH secretion in relation to that of follicle stimulating hormone (FSH) and prolactin, and suckling and ovarian activity at 4 and 8 weeks postpartum in 20 fully breastfeeding women with lactational amenorrhoea. Blood samples were withdrawn at 10 min intervals for 24 h from 0900 h to 0900 h at either 4 weeks (n = 9) or 8 weeks (n = 11) postpartum, while the mothers and babies continued their normal pattern of suckling activity. At 4 weeks postpartum, no LH pulses occurred over 24 h in six of the nine women while one (n = 1) or two (n = 2) LH pulses occurred in three of the nine women. In contrast, LH pulses were present in nine of the 11 women at 8 weeks postpartum. The pulse frequency varied considerably from two to eight pulses over the 24 h and there was no influence of the time of day or sleep on the time of the pulse release. Lactational amenorrhoea was maintained for at least 10 weeks afterwards and there was no relationship between the time of resumption of ovarian activity and the presence or absence of pulsatile LH secretion at 4 or 8 weeks postpartum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adolescent cocaine and injection stress effects on the estrous cycle

Chronic cocaine exposure during critical periods of development induces short- and long-term effects. During the pubertal period, the hypothalamic–pituitary–gonadal (HPG) axis undergoes many dynamic changes. The present study investigated whether chronic periadolescent cocaine alters reproductive maturity in the rat. Sixty female Long–Evans hooded rats were randomly assigned to one of three conditions (20 mg cocaine/kg/day, saline injected and uninjected), for dosing from postnatal day 21 (P21) through P60. Several indicators of reproductive maturation and functioning were assessed during and following treatment. Cocaine exposure had no effect on the onset of puberty or on the date of first ovulation. The number of proestrus–estrus transitions was significantly lower in cocaine-exposed females compared to uninjected females, but not compared to saline-injected controls. This reduction was observed during exposure to cocaine, as well as after the cessation of injections. During the dosing period, cocaine-exposed rats also exhibited a greater number of cycles that had no clear P–E transition than did UN subjects; this effect disappeared once injections stopped. These alterations suggest immediate, and possibly persisting, alterations in the control of ovulation after chronic cocaine exposure throughout adolescence. Interestingly, during the injection period, the saline-injected females had a significantly greater number of diestrus days compared to uninjected and cocaine-injected animals, as well as a lower proportion of regular 4- and 5-day cycles. These differences disappeared once injections stopped. These results suggest a stress-induced irregularity of the estrous cycle, possibly attenuated by cocaine and recoverable after exposure. The present findings indicate that the HPG axis is susceptible to short-term, and possibly to long-term, alterations induced by cocaine exposure throughout the adolescent period.     

The effects of immersion and exercise on prolactin during pregnancy

Summary Prolactin is an important hormone during pregnancy, affecting mother, fetus, and amniotic fluid volume. Immersion is known to affect prolactin levels significantly. To determine the effect of immersion and exercise on the prolactin response during pregnancy, we examined serum prolactin levels at 15, 25, and 35 weeks' gestation and 10 weeks post partum. Twelve women completed 20 min land rest, 20 min immersion in 30° C water to the xiphoid, and 20 min exercise in the water at 60% Resting prolactin levels were 1.91±0.32, 4.55±0.5, and 5.85±0.27 nmol·l^–1 ±standard error of the mean at 15, 25, and 35 weeks' gestation, respectively. Postpartum lactating women had a resting mean prolactin level of 3.95±1.6 versus 0.22±0.4 nmol· l^–1 in non-lacting women. Prolactin levels declined significantly during immersion even after correction for dilution by plasma volume shifts. The immersion response was inversely related to the duration of pregnancy with 29%, 22%, and 12% drops during 15-, 25- and 35-week trials, respectively. Compared to rest, exercise prolactin levels remained depressed during the 15th and 25th week trials. We hypothesize that immersion in water caused prolactin levels to decline.     

The role of prolactin in the development of chronic progressive nephropathy in the rat

Summary Prolactin as a factor in the etiology of chronic progressive nephropathy in rats has been studied by exogenous administration and by endogenous inhibition with bromocriptin. Exogenous prolactin caused a significant increase in frequency and severity of the lesions, with accompanying sodium retention. Conversely endogenous inhibition significantly decreased the frequency and severity of the lesions and increased urine volume, pH and sodium excretion. Thus prolactin is important in the etiology of this renal disease in rats.     

Changes in gonadotrophins and prolactin levels in isolated (seasonally or lactationally) anovular ewes associated with ovulation caused by the introduction of rams

The response of seasonally or lactationally anovular ewes to ram stimulation (teasing) was investigated in Ile-de-France (IF) and Prealpes (PA) ewes. In the first experiment (seasonally anovular IF and PA ewes) the possible role of prolactin (PRL) in the response to teasing was investigated by selective blockage of the secretion of PRL by CB 154 for 7 days before teasing. In the second experiment (lactationally anovular PA ewes) the role of PRL in the teasing response was investigated by studying ewes suckling one or two lambs, which presented differences in LH and PRL concentrations (p<0.025). In the first experiment, before teasing, basal concentration of LH and frequency of pulses were higher in PA than in IF ewes (p<0.001). The concentration of PRL was higher in IF ewes (p<0.001). Treatment by CB 154 did not affect the secretion of LH or FSH in either breed. Following the introduction of rams a rapid increase (<60 min) in concentration of LH, but not FSH, was observed, irrespective of breed or CB 154 treatment. In suckling ewes (Exp. 2) the frequency of pulses of LH was higher in ewes rearing one lamb than in ewes rearing twins (p=0.05). Stimulation by the rams resulted in a rapid increase (<40 min) in the pulsatile release of LH, irrespective of PRL concentration before teasing. In both experiments most ewes ovulated within 3 days of the start of the ram stimulation. It is concluded that PRL concentration does not affect the sensitivity of the brain to stimuli provided by rams. Analysis of hormonal patterns indicate also that hormonal events preceding ovulation are different from those observed in cyclic females.     

Comparison of the effects of repeated electroconvulsive shock on alpha 2- and beta-adrenoceptors in different regions of rat brain

The effects of ten, once-daily electroconvulsive shocks on alpha 2 and beta-adrenoceptor binding were investigated in the rat cortex, hippocampus, hypothalamus and cerebellum. [3H]Clonidine and [3H]dihydroalprenolol were used as radioligands for alpha 2 and beta-adrenoceptors respectively. Twenty-four hours after the last shock, the density of beta-adrenoceptors was reduced in the cortex and hippocampus, but not in the hypothalamus or cerebellum. There was no change in the apparent affinity of the beta-receptors in any of the regions studied. Alpha 2-adrenoceptor density was reduced in all the regions studied (cortex, hippocampus, hypothalamus) with, again, no change in their apparent affinity. It is concluded that the effects of electro-convulsive shock on alpha 2 and beta-adrenoceptors show regional variation; possible reasons for this variation are discussed.     

Electroconvulsive shock: Effects on sleep and cortical steady potential in the rat

Continuous ECoG, EMG and SP recordings were taken in rats prior and subsequent to ECS treatments. Slow-potential (SP) shifts associated with sleep and wakefulness were consistent in direction and predictable in occurrence before and after treatment. SP shifts accompanying the transition from quiet wakefulness to slow-wave sleep (SWS) and from SWS to paradoxical sleep (PS) were surface negative. Upon arousal, there was a positive shift to waking SP levels. A substantial increase in total sleep time (TST) accompanied by a reduction in PS persisted for 3 days following ECS. Thereafter, both TST and PS returned to baseline levels. A rebound in PS duration and frequency occurred at different times in different animals, but a significant overall rebound effect could not be demonstrated in the pooled data. All treatments elicited grand mal electrical and behavioral seizures. ECS-induced SP shifts were surface negative (4–8 mV) and lasted from 10–30 sec. In contrast to the SP stability prior to ECS, every animal underwent major aperiodic SP shifts after ECS. These were of greater magnitude and longer duration than those seen during pre-ECS sleep-wakefulness cycles.     

Age related changes in the control of prolactin secretion in the female rat

The purpose of this investigation was to evaluate the effects of advancing age on the control of pituitary prolactin secretion. The effects of dopaminergic inhibition and estrogen stimulation of pituitary prolactin secretion were tested both in vivo and in vitro. Estrogen stimulated prolactin secretion in both old and young animals, and elevated estrogen levels in old rats may be partially responsible for elevated prolactin levels. Oral L-DOPA administration induced cycles in old rats but had no effect on prolactin levels in either old or young rats. Injections of L-DOPA lowered prolactin in young but not in old rats, while apomorphine reduced prolactin levels in both groups. The pituitaries of young rats secrete more prolactin in vitro than old pituitaries, further supporting a decrease in hypothalamic DA turnover as a cause for elevated prolactin levels in old rats.     

Effects of mastectomy and vagotomy on grooming behavior of the rat: possible involvement of prolactin

Surgical interventions such as unilateral mastectomy or vagotomy affect plasma prolactin (PRL) levels. Right-side mastectomized rats exhibiting high levels of plasma PRL showed increased grooming behavior. Left-side mastectomized rats with low levels of plasma PRL performed poor grooming activity. Bilateral mastectomy that caused a slight increase in plasma PRL levels was followed by enhanced grooming behavior. Both left and right vagotomy resulted in a significant increase in plasma PRL levels. However, only left-side vagotomized rats exhibited increased levels of grooming behavior, while no difference between right-side vagotomized rats and controls occurred. It is possible that changes in plasma PRL levels induced by surgical interventions affect grooming activity of the rat. However, the hypothesis that the integrity of peripheral organs is important for the display of grooming behavior cannot be ruled out.     

Ultrastructure,immunohistochemistry and hormone release of pituitary adenomas in relation to prolactin production

Summary Fifteen cases of pituitary adenoma, 14 of which were associated with hyperprolactinemia, were studied by observation and granule morphometry of electron micrographs, immunohistochemistry and sequential observation of in vitro release with regard to hormone production, storage and secretion. Adenoma cells of 6 cases with marked elevation of plasma prolactin were sparsely granulated, showed characteristic ultrastrucures including the presence of small secretory granules, well developed Golgi and rough membranes, misplaced exocytosis, and positive or negative immunostaining for prolactin. These adenomas also showed vigorous release of the hormone into the circulation and/or culture medium. In vitro studies showed that negative immunostaining of adenoma cells did not preclude the production and secretion of the hormone. One densely granulated adenoma containing cells with numerous lactotroph type granules showed moderate release of prolactin into the circulation. In an acromegalic case associated with both high plasma growth hormone and prolactin, some cells were shown by immunohistochemistry to store both hormones. There were 4 adenomas which could not be shown to produce, store and secrete prolactin by any method available.Abbreviations Used in this Paper ACTH adrenocorticotropic hormone - -MSH -melanocyte stimulating hormone - hGH human growth hormone - hPRL human prolactin - LH luteinizing hormone - FSH follicle stimulating hormone - TSH thyroid stimulating hormone - TRH Thyrotropin-releasing hormone This work was supported in part by Grants-in-Aid for Cancer Research (No. 50-14) and for Specific Diseases (Disorder of Hypothalamic and Pituitary System) from the Ministry of Health and Welfare, and for Cancer Research (No. 401034) from the Ministry of Education, Science and Culture, Japan     

Effects of prolactin on Na−K-ATPase activity along the rat nephron

To test prolactin (PRL) action on osmoregulation in mammals, we evaluated in the rat the effect of this hormone on a major enzyme in renal regulation of water and electrolyte: renal Na–K-ATPase. Enzyme activity was determined by cytochemistry in medullary ascending limb (MAL) and distal convoluted tubule (DCT) from rats treated either by bromocriptine, or by PRL. Three hours after a bromocriptine injection (0.1 mg/100 g IP) a significant decrease of Na–K-ATPase activity is observed in both MAL (80% of control values,p<0.001) and DCT (78%,p<0.01). Reciprocally, a significant (p<0.001) increase in enzyme activity is induced 3 h after a single PRL injection (140 g/100 g IM), in both segments (MAL: 165%, DCT: 172% of control activities) and persists 6 h after the injection (MAL: 130%, DCT: 118%). Na–K-ATPase activity was correlated to plasma PRL levels (r=0.78 in DCT,r=0.89 in MAL). A direct effect of PRL on the tubule is suggested by results from experiments in which PRL, at various concentrations, is added in vitro on renal slices before Na–K-ATPase activity measurements. The increase in Na–K-ATPase activity exhibits a log-dose dependency with PRL concentration (p<0.01) and is still observed when AVP antagonist is added before PRL incubation, ruling out the possible role of AVP contamination of PRL. These results suggest a direct effect of PRL on renal Na–K-ATPase in MAL and DCT.     

Influence of the presence of rams on the timing of ovulation and discharge of LH in ewes

The influence of the presence of the male on the ovulation process was investigated in ewes after oestrus control by progestagens (intravaginal fluorogestone acetate) and PMSG. Permanent contact with the rams throughout oestrus accelerates the ovulation and the appearance of the LH surge. The results suggest that the action of the presence of the male on ovulation is mediated by way of the ovulatory surge of LH.