24-hour changes in circulating prolactin, follicle-stimulating hormone, luteinizing hormone, and testosterone in young male rats subjected to calorie restriction

This work analyzes the effect of calorie restriction on the 24 h variation of pituitary-testicular function in young male Wistar rats by measuring the circulating levels of prolactin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone. Control animals were provided an equilibrium calorie diet and the experimental animals a calorie-restriction diet equivalent to 66% of food restriction for four weeks starting on day 35 of life. Different groups of control and experimental rats were killed at 6 h intervals around the clock, beginning 1 h after light on (HALO). Compared to the control animals, the mean secretion of prolactin was augmented and that of LH and testosterone decreased in calorie-restricted rats, whereas FSH release remained unchanged. Significant changes in the 24 h secretory pattern of circulating prolactin, LH, and testosterone occurred in the calorie-restricted rats. These include the appearance of a second maximum of plasma prolactin at 21 HALO, blunting of the LH peak seen at 13 HALO, and phase-shift of the testosterone peak from 13 HALO in controls to 17 HALO in calorie-restricted rats. The significant positive correlation between individual LH and testosterone levels found in controls was no longer observed in calorie-restricted rats. Availability of nutrients presumably affects the mechanisms that modulate the circadian variation of the pituitary-gonadal axis in growing male rats.     

Age-dependent changes in 24-hour rhythms of catecholamine content and turnover in hypothalamus, corpus striatum and pituitary gland of rats injected with Freund's adjuvant

Background  

Little information is available on the circadian sequela of an immune challenge in the brain of aged rats. To assess them, we studied 24-hour rhythms in hypothalamic and striatal norepinephrine (NE) content, hypothalamic and striatal dopamine (DA) turnover and hypophysial NE and DA content, in young (2 months) and aged (18–20 months) rats killed at 6 different time intervals, on day 18^th after Freund's adjuvant or adjuvant's vehicle administration.     

Serum luteinizing hormone follicle-stimulating hormone and prolactin in neonatal-androgenized rats.

Serum levels of LH, FSH, Prolactin and Testosterone of 90 days old male rats androgenized soon after birth were determined by specific radioimmunoassay and were compared to untreated rats. LH and FSH levels were also determined in 90 days old female rats neo-natally treated with testosterone and compared with normal diestrus rats. Androgenization of male rats significantly increased serum FSH and Prolactin levels without producing changes in plasma LH and testosterone concentrations. Similar increase in the FSH levels were found in androgenized female rats although plasma FSH concentrations were lower than in the male groups. These results obtained in male rats give an additional evidence that androgens acting in the first days of life are responsible of the higher levels of FSH and Prolactin that characterize the male or tonic pattern of gonadotrophin secretion.     

Twenty-four hour rhythms of hypothalamic corticotropin-releasing hormone, thyrotropin-releasing hormone, growth hormone-releasing hormone and somatostatin in rats injected with Freund's adjuvant

The effect of Freund's adjuvant injection on 24-hour variation of hypothalamic corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH), GH-releasing hormone (GRH) and somatostatin levels was examined in adult rats kept under light between 0800 and 2000 h daily. Groups of rats receiving Freund's complete adjuvant or its vehicle 3 days before sacrifice were killed at six different time intervals throughout a 24-hour cycle. In the median eminence, adjuvant vehicle-injected rats exhibited significant 24-hour variations for the four hormones examined, with maxima at noon. These 24-hour rhythms were inhibited or suppressed by Freund's adjuvant injection. In the anterior hypothalamus of adjuvant vehicle-treated rats, CRH content peaked at 1600 h, while two peaks were found for TRH and GRH levels, i.e., at 2400-0400 h and 1600 h. Freund's adjuvant injection suppressed 24-hour rhythm of anterior hypothalamic CRH, TRH and GRH content and uncovered a peak in anterior hypothalamic somatostatin levels at 0400 h. In the medial hypothalamus of adjuvant vehicle-treated rats, significant 24-hour variations were detectable for TRH (peaks at 1600 and 2400 h) and somatostatin (peak at 2400 h) which disappeared after Freund's adjuvant injection. In the posterior hypothalamus of adjuvant vehicle-treated rats, two peaks were apparent for CRH, TRH and somatostatin levels, i.e. at 1600 h and 2400-0400 h, this hormonal profile remaining unmodified after Freund's adjuvant administration. The administration of the immunosuppressant drug cyclosporine (5 mg/kg, 5 days) impaired the depressing effect of Freund's adjuvant injection on CRH, TRH and somatostatin content in median eminence, but not that on GRH. In the anterior hypothalamus, cyclosporine generally prevented the effect of immunization on hormone levels an revealed a second maximum in TRH at 0400 h. Cyclosporine also restored 24-hour variations in TRH and somatostatin levels of medial hypothalamus of Freund's adjuvant-injected rats but was unable to modify them in the posterior hypothalamus. The results further support the existence of a significant effect of immune-mediated inflammatory response at an early phase after Freund's adjuvant injection on hypothalamic levels which was partially sensitive to immunosuppression by cyclosporine.     

Effects of prolonged treatment with diltiazem on pituitary secretion of luteinizing hormone, follicle-stimulating hormone, thyrotropin and prolactin.

In previous studies it has been observed that acute administration or short-term treatment with calcium channel blockers can influence the secretion of some pituitary hormones. In this study, we have examined the effect of the long-term administration of diltiazem on luteinizing-hormone (LH), follicle-stimulating hormone (FSH), thyrotropin (TSH) and prolactin (PRL) levels under basal conditions and after gonadotropin-releasing hormone (GnRH)/thyrotropin-releasing-hormone (TRH) stimulation in 12 subjects affected by cardiovascular diseases who were treated with diltiazem (60 mg 3 times/day per os) for more than 6 months and in 12 healthy volunteers of the same age. The basal levels of the studied hormones were similar in the two groups. In both the treated patients and the control subjects, a statistically significant increase (p < 0.01) in LH, FSH, TSH and PRL levels was observed after GnRH/TRH administration. Comparing the respective areas under the LH, FSH, TSH and PRL response curves between the two groups did not present any statistically significant difference. These findings indicate that long-term therapy with diltiazem does not alter pituitary hormone secretion.     

Ontogeny of growth hormone, prolactin, luteinizing hormone, and testosterone secretory patterns in the ram

The ontogenetic changes that occur in secretory patterns of growth hormone (GH), prolactin (Prl), luteinizing hormone (LH), and testosterone (T) in rams maintained in constant photoperiod were examined. Nine ram lambs were moved to individual pens in a controlled environment (12L: 12D cycle; 18-24 degrees C temperature) at 66 days of age. Blood samples were collected via indwelling cannulae at 15-min intervals for an 8-h period at 80, 136, 192, 248, and 304 days of age. Plasma concentrations of GH, Prl, LH, and T were quantitated and parameters of the secretory patterns determined. Mean concentration of GH tended to decline with age, probably because the amplitude of secretory peaks was significantly reduced with age. There were no age-associated changes in basal concentration of GH or incidence of GH peaks. There was an increase in Prl secretion (as estimated by mean concentration) at 136 and after 248 days of age. Significant age-associated changes occurred in all parameters of LH and T secretion. At the younger ages, testosterone concentrations were low and LH concentrations were elevated. At the older ages the relationship was reversed, with LH low and testosterone high. There were no significant correlations between frequency and magnitude of LH and T peaks. The significant correlations present among parameters of LH and T secretion were between basal concentration of LH and overall mean concentration and basal concentration of T. These results suggest that LH may not be the sole tropic stimulator of acute T secretion.     

Photoperiod entrainment of testosterone, luteinizing hormone, follicle-stimulating hormone, and prolactin cycles in rams in relation to testis size and semen quality

Adult rams were exposed to photoperiod treatments over 2 years to study the influence of light regimes on pituitary-testicular activity and semen quality. Initially, all rams (12 per group) were exposed to 3 months of long days (16L:8D). Group 1 was then exposed to a regime of continuous short days (8L:16D) and Groups 2, 3, and 4 were exposed to 4 months of short days alternated with 1, 2, or 4 months, respectively, of long days. Every 2 weeks, serum hormone levels and scrotal circumference were determined and semen quality was evaluated. Regular cycles in pituitary and testicular activities corresponding to the period of the lighting regime resulted in Groups 2, 3, and 4, but not in Group 1. In general, the change from long days to short days induced increases in follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone levels, scrotal size and sperm numbers and a decrease in prolactin. The reverse occurred after subsequent exposure to long days. After 4 months of long days, testicular regression was complete, but when long-day exposure was reduced, less regression occurred. With continuous exposure to short days, FSH and testosterone remained above basal levels, prolactin levels were depressed, scrotal size remained near the maximum, and elevated numbers of motile sperm were sustained.     

Effect of diclofenac on plasma levels of immunoreactive prolactin, follicle stimulating hormone, luteinizing hormone, thyrotropin, and beta-endorphin in humans

Prostaglandins have been shown to modulate the secretion of several pituitary hormones, suggesting that therapeutic doses of nonsteroidal anti-inflammatory drugs may change basal hormone levels. In this study, plasma levels of prolactin, follicle stimulating hormone, luteinizing hormone, thyrotropin and beta-endorphin were determined in 6 healthy men after administration of diclofenac, a prostaglandin synthesis inhibitor. The subjects were given 75 mg intramuscularly and 50 mg orally at 08.00 h the first day, 50 mg orally at 08.00, 12.00 and 20.00 h the second day and an additional 50 mg orally at 08.00 h the third day. Blood samples were collected throughout these 3 days. Diclofenac resulted in a significant and sustained decrease in plasma level of prolactin (p less than 0.005). The other hormones did not demonstrate significant change following diclofenac administration. These data suggest that administration of a prostaglandin synthesis inhibitor, such as diclofenac, selectively alters basal pituitary secretion of prolactin in humans without a detectable effect on plasma levels of other pituitary hormones. This study supports the hypothesis that prostaglandins are necessary for maintaining basal level of prolactin secretion in man.     

The effects of intracerebroventricular infusion of prolactin in luteinizing hormone, testosterone and growth hormone secretion in male sheep

This study tested a hypothesis that the enhancement of the prolactin (PRL) concentration within the central nervous system (CNS) disturbs pulsatile luteinizing hormone (LH) and growth hormone (GH) secretion in rams that are in the natural breeding season. A 3h long intracerebroventricular (icv.) infusion of ovine PRL (50 microg/100 microl/h) was made in six rams during the daily period characterized by low PRL secretion in this species (from 12:00 to 15:00 h); the other six animals received control infusions during the same time. Blood samples were collected from 9:00 to 18:00 h at 10 min intervals. A clear daily pattern of LH secretion was shown in control animals, with the lowest concentration at noon and an increasing basal level around the time of sunset (P < 0.001). No significant changes in LH concentration occurred in PRL-infused animals and the concentration noted after infusion of PRL was significantly (P < 0.05) lower than after the control infusion. The frequency of LH pulses tended to decrease in rams after PRL treatment. The changes in LH secretion clearly carried over to the secretion of testosterone in the rams of both groups. The GH concentrations changed throughout the experiment in both groups of rams, being higher after the infusions (P < 0.001). However, the mean GH concentration and GH pulse amplitude noted after PRL infusion were significantly lower (P < 0.001 and P < 0.05, respectively) from those recorded in the control. The continued fall in PRL secretion observed in rams following PRL infusion (P < 0.05 to P < 0.001) indicates a high degree of effectiveness of exogenous PRL at the level of the CNS. In conclusion, maintenance of an elevated PRL concentration within the CNS leads to disturbances in the neuroendocrine mechanisms responsible for pulsatile LH and GH secretion in sexually active rams.     

Effect of octreotide on 24-hour growth hormone and prolactin secretory patterns in acromegalics.

Four adult patients with active acromegaly underwent studies of their 24-hour secretory pattern of hGH and Prl prior to and at the end of 3 months of treatment with the octreotide (somatostatin analog SMS 201-995) 100 micrograms s.c. every 8 h. Blood was withdrawn at 30-min intervals with the aid of a constant withdrawal pump. The best fit cosinor method was used to define the following rhythm parameters: mesor, amplitude, acrophase and periodicity. Prior to treatment, hGH secretion was increased in all patients. The mean 24-hour ranged from 9-47 ng/ml with amplitude 5.2-23 and observed maximal pulse 41-95 ng/ml. Computed rhythms were circadian in 3 patients and ultradian in 1; in 2 patients the acrophases were shifted to daytime. hPrl secretion was altered in 3 of the patients. Two had elevated mean 24-hour of 17.7 and 22.2 ng/ml, while computed rhythms showed semicircadian periodicity in 1 of them and circadian periodicity with a shift of acrophase to daytime in the other. The third patient who had normal hPrl levels, showed ultradian 8-hour periodicity. At the end of treatment there was a marked reduction in hGH secretion in 1 patient and a lesser reduction in the other 3. The rhythm was influenced by the masking effect of the drug, to yield an 8-hour period with acrophases related to injection clock time having equal amplitudes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of exogenous testosterone on testicular luteinizing hormone and follicle-stimulating hormone receptors during aging

During aging, the male Japanese quail exhibits a loss of fertility, increased morphological abnormalities in the testes, and a higher incidence of Sertoli cell tumors. Although there is a coincident loss of reproductive behavior, plasma androgen levels remain high until testicular regression occurs in association with senescence. The purpose of this study was to compare mean specific binding of chicken luteinizing hormone (LH) and follicle-stimulating hormone (FSH) as a measure of testicular receptors during identified stages during aging. Males were categorized according to age (young = 9 months, middle aged = 24 months, or old = 36+ months) and sexual behavior (active or inactive). Testicular samples were collected immediately after perfusion with 4% paraformaldehyde from the following groups: young active (n = 8), young photoregressed (n = 5), young photoregressed plus testosterone implant (n = 4), middle-aged active (n = 8), middle-aged inactive (n = 4), old inactive (n = 5), and old inactive plus testosterone implant (n = 6). A crude plasma membrane fraction was prepared from the testes of each bird and an aliquot deriving from 10 mg of testicular tissue was used for binding assay. Specific binding of labeled LH or FSH was expressed as percentage of total radioactive hormone. Results showed significant (P < 0.05) age-related decreases in both FSH and LH receptor numbers. The highest FSH binding was found in young and middle-aged active males, with low binding in old inactive males. Testicular LH binding decreased during aging, with a sharp decrease in middle-aged males, which was similar to old males. Testosterone implants weakly stimulated FSH and LH binding in old males. Both LH and FSH binding decreased in photoregressed young males. However, testosterone implants stimulated increased LH binding, but did not affect FSH binding in young photoregressed males. These results provide evidence for separate regulation of testicular LH and FSH receptors, with testosterone stimulation of LH receptor, but not FSH receptor number in young males. However, during aging there appears to be a loss of this response, potentially because of the reduced efficacy of testosterone stimulation, thereby implying a diminished capacity for response with aging.     

Puberty in the male chimpanzee: time-related variations in luteinizing hormone, follicle-stimulating hormone, and testosterone

The onset of pubertal testicular growth (Po) occurred in 12 out of 20 male chimpanzees surveyed monthly for at least 3.7 yr. When animals were synchronized according to Po, the mean weight gain was found to be higher before than after Po, and testicular volume started to rise immediately after Po. The earlier significant hormonal events were a rapid rise in LH and a slight testosterone increase occurring 6 mo before Po. Thereafter, the levels of LH remained elevated while testosterone continued to rise in parallel with the testicular volume. FSH levels increased suddenly at Po, 6 mo after the LH increase. FSH remained elevated for only 9 mo, then dropped to prepubertal levels. The dissociation between onsets of pubertal increases in LH and FSH secretions suggests that the complete reawakening of the hypothalamic-pituitary unit lasts several months. The secondary drop of FSH, occurring at the time of spermarche, may be induced by factor(s) secreted by the testis.     

Effects of thermal stress on plasma concentrations of luteinizing hormone, progesterone, prolactin and testosterone in the cycling ewe

Naturally cycling white faced ewes were utilized to study the effects of continuously elevated environmental temperature and/or humidity on plasma concentrations of luteinizing hormone (LH), prolactin (PRL), progesterone (P4) and testosterone (TE) during the estrous cycle. Fourteen ewes were randomly allocated on the day of estrus (day 0) to either thermoneutral conditions (21.1 degrees C, 65% relative humidity) or elevated ambient temperature/humidity conditions (36.1 degrees C, 71% relative humidity) producing an average 1.4 degrees C hyperthermia. Animals remained in their respective environments and blood samples were collected daily until the next estrus or day 20, whichever occurred first. Starting at noon on day 14, blood was sampled every 2 hours. Concentrations of LH, PRL, P4 and TE were quantified using validated radioimmunoassays. Hyperthermic ewes exhibited 1) a significant decrease (P<0.05) in the incidence of behavioral estrus and a preovulatory LH surge at the expected time of the estrous cycle, 2) significantly lower (P<0.05) plasma P4 between days 7 and 13 of the cycle, 3) a six-fold increase of PRL levels (P<0.01). Plasma levels of TE were not significantly affected by hyperthermia. The only two experimental ewes which exhibited estrus and an LH surge also showed an unusual and significant peak in plasma P4 two days before estrus. These results confirm that elevated environmental temperatures that result in hyperthermia can induce endocrine imbalances in the ewe which may contribute to decreased reproductive efficiency in the heat-stressed female.     

Effect of rabbit doe-litter separation on 24-hour changes of luteinizing hormone,follicle stimulating hormone and prolactin release in female and male suckling pups

Background  

The daily pattern of nursing of the rabbit pup by the doe is the most important event in the day for the newborn and is neatly anticipated by them. Such anticipation presumably needs a close correlation with changes in hormones that will allow the pups to develop an appropriate behavior. Although a number of circadian functions have been examined in newborn rabbits, there is no information on 24-h pattern of gonadotropin release or on possible sex-related differences in gonadotropin or prolactin (PRL) release of pups. This study examined the 24-h changes of plasma luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) in 11 days old suckling female and male rabbits left with the mother or after short-term (i.e., 48 h) doe-litter separation.     

Effects of cranial cervical ganglionectomy and castration of male lambs. II. 24 hour plasma profiles of luteinizing hormone, testosterone and prolactin

Male lambs were utilized in an experiment designed to evaluate the effects of cranial cervical ganglionectomy (GX), castration and age on hormone secretion profiles. Blood plasma samples were collected at hourly intervals for 24 hours from 24 lambs aged 101 days and 20 lambs aged 277 days, then assayed for concentrations of luteinizing hormone (LH), testosterone and prolactin. At both ages pulsatile secretion of LH and testosterone was confirmed, but no circadian rhythm of LH testosterone or prolactin secretion was detected. Castration elevated LH levels significantly at both ages. GX and its interaction with castration had no effect on LH secretion at 101 days, but at 277 days these factors were significant, largely due to elevated levels being recorded from GX castrates. GX did not affect testosterone levels in entire animals at either age, while plasma from castrates contained no detectable testosterone. GX reduced prolactin concentrations at 101 days of age (summer) but elevated them at 277 days of age (winter). Castration and the interaction of castration with GX had no significant influence on plasma prolactin levels at either age. This study confirmed that the pineal gland of sheep is involved in the regulation of prolactin secretion, and probably influences LH secretion as well.     

Effects of gonadotropin-releasing hormone pulse-frequency modulation on luteinizing hormone, follicle-stimulating hormone and testosterone secretion in hypothalamo/pituitary-disconnected rams

The effects of changes in pulse frequency of exogenously infused gonadotropin-releasing hormone (GnRH) were investigated in 6 adult surgically hypothalamo/pituitary-disconnected (HPD) gonadal-intact rams. Ten-minute sampling in 16 normal animals prior to HPD showed endogenous luteinizing hormone (LH) pulses occurring every 2.3 h with a mean pulse amplitude of 1.11 +/- 0.06 (SEM) ng/ml. Mean testosterone and follicle-stimulating hormone (FSH) concentrations were 3.0 +/- 0.14 ng/ml and 0.85 +/- 0.10 ng/ml, respectively. Before HPD, increasing single doses of GnRH (50-500 ng) elicited a dose-dependent rise of LH, 50 ng producing a response of similar amplitude to those of spontaneous LH pulses. The effects of varying the pulse frequency of a 100-ng GnRH dose weekly was investigated in 6 HPD animals; the pulse intervals explored were those at 1, 2, and 4 h. The pulsatile GnRH treatment was commenced 2-6 days after HPD when plasma testosterone concentrations were in the castrate range (less than 0.5 ng/ml) in all animals. Pulsatile LH and testosterone secretion was reestablished in all animals in the first 7 days by 2-h GnRH pulses, but the maximal pulse amplitudes of both hormones were only 50 and 62%, respectively, of endogenous pulses in the pre-HPD state. The plasma FSH pattern was nonpulsatile and FSH concentrations gradually increased in the first 7 days, although not to the pre-HPD range. Increasing GnRH pulse frequency from 2- to 1-hour immediately increased the LH baseline and pulse amplitude. As testosterone concentrations increased, the LH responses declined in a reciprocal fashion between Days 2 and 7. FSH concentration decreased gradually over the 7 days at the 1-h pulse frequency. Slowing the GnRH pulse to a 4-h frequency produced a progressive fall in testosterone concentrations, even though LH baselines were unchanged and LH pulse amplitudes increased transiently. FSH concentrations were unaltered during the 4-h regime. These results show that 1) the pulsatile pattern of LH and testosterone secretion in HPD rams can be reestablished by exogenous GnRH, 2) the magnitude of LH, FSH, and testosterone secretion were not fully restored to pre-HPD levels by the GnRH dose of 100 ng per pulse, and 3) changes in GnRH pulse frequency alone can influence both gonadotropin and testosterone secretion in the HPD model.     

Lithium-induced changes in the plasma and pituitary levels of luteinizing hormone,follicle stimulating hormone and prolactin in rats

Adult male Sprague-Dawley rats, maintained under a controlled photoperiod of LD 14:10 (white lights on at 06:00 h, CST), were injected with lithium chloride and changes in the levels of plasma and pituitary homogenates of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL) were examined to evaluate the effects of this anti-manic drug on reproductive function. Two groups of rats were injected with lithium chloride intraperitoneally, twice daily at 09:00 and 16:00 h, for 2 and 7 days at a dosage of 2.5 meg/Kg body weight. Plasma and pituitary levels of LH, FSH and PRL were measured by radioimmunoassay. Plasma levels of LH were significantly (P<0.05) increased after 2 days of lithium treatment. In contrast, a significant (P<0.005) reduction in plasma levels of LH was evident when lithium injections were continued for 7 days. The plasma levels of FSH remained unaffected by lithium treatment by either time period. Lithium administered for 2 days did not bring about any significant alteration in the plasma levels of PRL, although there was a significant (P<0.002) reduction in plasma PRL levels after 7 days treatment. The concentrations of pituitary LH, FSH and PRL remained unchanged after 2 and 7 days of lithium treatment.