Effect of p-chlorophenylalanine on LH, FSH, prolactin and ovulation in the rat

The effect of p-chlorophenylalanine (PCPA: 300 mg/kg) on the rate of ovulation and plasma LH, FSH and prolactin secretion has been studied in rats at preovulatory periods (18th hour of diestrus) and post-ovulatory periods (9th hour of metaestrus). In both experimental groups, results showed that administration of PCPA caused an increase in both prolactin concentration and number of mature ovarian follicles (p less than 0.001). No changes were observed in FSH levels. LH concentration, however, decreased (p less than 0.001) and ovulation became totally inhibited. Rats treated at the 9th hour of metaestrus exhibited a marked luteinization as well as an increased number of corpus luteum in the ovaric tissue (p less than 0.001), whereas those treated at the 18th hour of diestrus underwent no luteinization and merely showed a greater number of mature ovarian follicles (p less than 0.001). PCPA, therefore, seems not to have a double effect on ovulation, LH, FSH, and prolactin secretion regardless of the pre or post-ovulatory periods. Changes observed in the ovaric tissue might be due to an increase in plasma prolactin concentration which appears earlier in the preovulatory than in the post-ovulatory treated animals. This difference may explain the double effect that has been attributed to the ovaric cycle and reproductive behavior.     

Comparative effects of LHRH agonist and ovine LH administration on testicular steroidogenesis in intact adult rat

In order to better understand the effects of LHRH administration on testicular function in adult rat, we compared the inhibitory effects of LH and the LHRH analogue [D-Ser-(TBU)⁶, des-Gly-NH₂ ¹⁰]LHRH ethylamide upon testicular steroidogenesis and LH, FSH and prolactin receptor contents. Administration of LH as well as LHRH analogue resulted in a marked decrease of LH receptor levels, accompanied by a blockage at the level of 17-hydroxylase activity. We have been able to demonstrate that multiple LH administration can achieve a testicular desensitization comparable to that observed after LHRH agonist treatment.     

Changes in rat ovaries of specific binding for LH, FSH and prolactin during the oestrous cycle and pregnancy.

In cyclic rats, the highest ovarian specific binding for LH was 6-0+/- 2-2% inpro-oestrus. During pregnancy, the specific binding of 125I-labelled bovine LH by rat ovaries increased gradually and reached a maximum of 24-1+/-4-9% between Days 14 and 18 of gestation; a slight decrease in binding was observed at Day 20 of pregnancy. Ovarian specific binding for FSH was also highest in pro-oestrus (8-9+/-2-1%), decreasing to about 50% in oestrus and metoestrus, but staying relatively constant during pregnancy. For prolactin, the specific binding in rat ovaries was highest (7-1+/-1-6%) in pro-oestrus, quite high in metoestrus and dioestrus and low in oestrus. Specific binding increased gradually only after Day 14 of pregnancy. Serum concentrations of rat LH, FSH and prolactin at different stages of the oestrous cycle and during pregnancy were determined by radioimmunoassays, and no obvious correlation was observed between levels of circulating hormones and the specific binding of these hormones in ovarian tissues. Affinity constants (Ka) for the hormones were very similar between ovaries from pro-oestrous rats and late-pregnant rats, being 0-31 X 10(9) M-1 for LH, 0-65 X 10(10)M-1 for FSH, and 1-14 X 10(10)M-1 for prolactin. Increases in specific binding for different hormones were due to increases of total binding sites in the ovary under different physiological states.     

Effects of oestradiol on LH, FSH and prolactin in ovariectomized ewes

This study was conducted to test the hypothesis that the rate (dose/time) at which oestradiol-17 beta (oestradiol) is presented to the hypothalamo-pituitary axis influences secretion of LH, FSH and prolactin. A computer-controlled infusion system was used to produce linearly increasing serum concentrations of oestradiol in ovariectomized ewes over a period of 60 h. Serum samples were collected from ewes every 2 h from 8 h before to 92 h after start of infusion, and assayed for oestradiol, LH, FSH and prolactin. Rates of oestradiol increase were categorized into high (0.61-1.78 pg/h), medium (0.13-0.60 pg/h) and low (0.01-0.12 pg/h). Ewes receiving high rates of oestradiol (N = 11) responded with a surge of LH 12.7 +/- 2.0 h after oestradiol began to increase, whereas ewes receiving medium (N = 15) and low (N = 11) rates of oestradiol responded with a surge of LH at 19.4 +/- 1.7 and 30.9 +/- 2.0 h, respectively. None of the surges of LH was accompanied by a surge of FSH. Serum concentrations of FSH decreased and prolactin increased in ewes receiving high and medium rates of oestradiol, when compared to saline-infused ewes (N = 8; P less than 0.05). We conclude that rate of increase in serum concentrations of oestradiol controls the time of the surge of LH and secretion of prolactin and FSH in ovariectomized ewes. We also suggest that the mechanism by which oestradiol induces a surge of LH may be different from the mechanism by which oestradiol induces a surge of FSH.     

On the correlation between FSH, LH and prolactin serum levels.

In 188 males FSH, LH, and prolactin serum levels determined from a single blood sample were found to be closely correlated. No correlation appeared to testosterone levels. The same correlation is observed, if serum levels of FSH, LH, and prolactin are measured after stimulation with LH-RH and TRH. In order to explain the close correlation, in five young men hormone levels were measured at 2-min-intervals over a period of 2 hours. Peaks of prolactin often correspond to those of FSH and LH, and a statistical correlation was found in two cases between FSH and prolactin. Results suggest a common releasing mechanism, which is superposed to the main mediating mechanism.     

Seasonal variations of LH, prolactin, androstenedione, testosterone and testicular FSH binding in the male blue fox (Alopex lagopus)

The seasonal changes in testicular weight in the blue fox were associated with considerable variations in plasma concentrations of LH, prolactin, androstenedione and testosterone and in FSH-binding capacity of the testis. An increase in LH secretion and a 5-fold increase in FSH-binding capacity were observed during December and January, as testis weight increased rapidly. LH levels fell during March when testicular weight was maximal. Plasma androgen concentrations reached their peak values in the second half of March (androstenedione: 0.9 +/- 0.1 ng/ml: testosterone: 3.6 +/- 0.6 ng/ml). A small temporary increase in LH was seen in May and June after the breeding season as testicular weight declined rapidly before levels returned to the basal state (0.5-7 ng/ml) that lasted until December. There were clear seasonal variations in the androgenic response of the testis to LH challenge. Plasma prolactin concentrations (2-3 ng/ml) were basal from August until the end of March when levels rose steadily to reach peak values (up to 13 ng/ml) in May and June just before maximum daylength and temperature. The circannual variations in plasma prolactin after castration were indistinguishable from those in intact animals, but LH concentrations were higher than normal for at least 1 year after castration.     

Effects of the intraventricular administration of 5,7-dihydroxytryptamine on FSH, LH and prolactin secretion in neonatally estrogenized male rats

The role of the serotoninergic system in the control of LH, FSH and prolactin secretion was analyzed in control and neonatally estrogenized male rats. Animals injected s.c. with 500 micrograms of estradiol benzoate (EB) on day 1 of life, or their corresponding sham-treated controls, were divided on day 75 into the following groups: (1) orchidectomized; (2) injected intraventricularly with 5,7-dihydroxytryptamine (5,7-DHT); (3) orchidectomized and treated with 5,7-DHT, and (4) sham operated. 15 days later, the animals were decapitated and their FHS, LH and prolactin plasma values measured by specific RIA systems. After the treatment with 5,7-DHT, control animals showed a decline in basal prolactin levels but no modification in basal LH and FSH values. After castration, 5,7-DHT-treated animals showed a reduced LH increase and a more marked prolactin decrease. In neonatal estrogen-treated animals, the 5,7-DHT injection did not change FSH, LH or prolactin levels but did partially or completely abolish the post-castration rise in FSH and LH levels, respectively. These data seem to indicate that neonatal estrogenization induced a modification of the serotoninergic role in the control of LH, FSH and prolactin.     

Low serum levels of FSH, LH and prolactin in luteal phase inadequacy

In order to elucidate the relationship between prolactin (PRL) levels and corpus luteum function in humans, assessment of temporal relationship between levels of PRL, LH, FSH, estradiol and progesterone was made in eleven normal cycling women and six short luteal women. All hormones were determined by specific radioimmunoassay. The mean PRL level in the luteal phase was higher than that in the follicular phase in normal women. On the other hand, no difference mean was seen between the PRL levels of follicular and luteal phases in short luteal women. In addition, follicular and luteal phase secretion of PRL in the short luteal phase (SLP) was lower than that in the normal control. LH and FSH in the follicular and luteal phases, estradiol secretion in the late follicular and early to mid-luteal phases in SLP were also lower than those in the control. These observations were consistent with the hypothesis that SLP is a sequel to aberrant folliculogenesis. In addition, it is inferred that low PRL levels in the SLP might be due to inadequate augmentation by estrogen, rather than giving PRL any positive controlling role in the maintenance of corpus luteum function.     

Effect of specific FSH or LH deprivation on testicular function of the adult rat.

While the need for FSH in initiating spermatogenesis in the immature rat is well accepted, its requirement for maintenance of spermatogenesis in adulthood is questioned. In the current study, using gonadotropin antisera to neutralize specifically either endogenous FSH or LH, we have investigated the effect of either FSH or LH deprivation for a 10-day period on (i) testicular macromolecular synthesis in vitro, (ii) the activities of testicular germ cell specific LDH-X and hyaluronidase enzymes, and finally (iii) on the concentration of sulphated glycoprotein (SGP-2), one of the Sertoli cell marker proteins. Both immature (35-day-old) and adult (100-day-old) rats have been used in this study. Since LH deprivation leads to a near total blockade of testosterone production, the ability of exogenous testosterone supplementation to override the effects of LH deficiency has also been evaluated. Deprivation of either of the gonadotropins significantly affected in vitro RNA and protein synthesis by both testicular minces as well as single cell preparations. Fractionation of dispersed testicular cells preincubated with labelled precursors of RNA and protein on Percoll density gradient revealed that FSH deprivation affected specifically the rate of RNA and protein synthesis of germ cell and not Leydig cell fraction. LH but not FSH deprivation inhibited [3H]thymidine incorporation into DNA. The inhibitory effect of LH could mostly be overriden by testosterone supplementation. LDH-X and hyaluronidase activities of testicular homogenates of adult rats showed significant reduction (50%; P less than .05) following either FSH or LH deprivation. Again testosterone supplementation was able to reverse the LH inhibitory effect.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of photoperiod on LH, FSH and prolactin patterns in ovariectomized oestradiol-treated heifers

Angus and Angus crossbred heifers were ovariectomized, treated with oestradiol implants and randomly assigned to the natural photoperiod of fall to spring for 43 degrees N latitude or extra light simulating the photoperiod of spring to fall. Weekly blood samples were taken for 6 months (fall to spring equinox). All heifers were cannulated every 4 weeks and blood samples were taken for 4 h at 15-min intervals. Sera were assayed for LH, FSH, prolactin and oestradiol. In samples taken weekly, serum LH and FSH concentrations were higher while serum prolactin was lower in heifers exposed to natural photoperiod. There was a photoperiod X time interaction for both FSH and prolactin with concentrations diverging as photoperiod diverged. Circulating concentrations of oestradiol were not different between groups. In samples taken every 4 weeks at 15-min intervals, baseline concentrations of LH and FSH and LH pulse amplitude were higher while prolactin pulse frequency was lower in heifers exposed to natural photoperiod. There was a photoperiod X time interaction for each of these pulsatile characteristics. The correlation between LH and prolactin concentrations estimated from the 15-min samples differed between the two photoperiod treatment groups. The pooled correlation coefficient (r) was -0.12 under natural photoperiod and +0.50 under extra light. There was also a photoperiod X time interaction with negative correlations occurring when photoperiod was decreasing and positive correlations occurring when photoperiod was increasing. These results support the hypothesis that photoperiod alters serum concentrations of LH, FSH and prolactin in cattle.