Biomedical subjects

R R Gala

Publications and source records attributed to R R Gala.

At least 55 records · Page 3Linked to original sources

PubMed1985

Central nervous system regions involved in the estrogen-induced afternoon prolactin surge. II. Implantation studies.

In the intact cycling female rat, there is a surge of plasma PRL during the afternoon of proestrus. Ovariectomy on diestrous day 1 eliminated the PRL surge completely, and injection of 100 micrograms polyestradiol phosphate, a long-acting estrogen, not only maintained the surge, but amplified and prolonged it. Bilateral implantation of an estradiol (E2)-containing cannula [diluted 1:4 with cholesterol (C)] in the medial preoptic area (MPO), but not in the cerebral cortex (CC), also maintained the surge. In long term ovariectomized rats, bilateral implantation of E2-containing cannulae (1:5, 1:10, 1:20, and 1:200) in the corticomedial amygdala (CMA) or ventromedial nucleus of the hypothalamus or a singular implantation in the third ventricle failed to induce a PRL surge 12 days later. Similar singular implantation in the anterior pituitary (AP) increased the basal levels of plasma PRL compared to those in C-implanted controls, but no surge was evident. Only bilateral implantation of E2 in the MPO induced a small but significant rise of plasma PRL at 1700 and 1900 h. Using higher concentration implants with a higher E2 concentration (1:4) in the MPO and sampling at shorter intervals, significant afternoon PRL surges were induced on days 2-4. However, systemic effects of E2, i.e. vaginal cornification and uterine weight enlargement, were also evident. Similar implants in other brain regions had the same results. Further increasing the E2 to C dilution from 1:10 to 1:200 eliminated the systemic effect of E2 implants, while the PRL surge-inducing ability persisted. It appears that the highest diluted E2 implants (1:150 and 1:200) gave the highest PRL response and persisted for the greatest number of days. Using the highly diluted E2 implants (1:100 and 1:200) in various brain regions, the MPO and the ventromedial hypothalamus were the most sensitive areas in inducing the PRL surge; the other areas studied, including suprachiasmatic nuclei, CMA, AP, and CC were ineffective. In conclusion, highly diluted E2 implants in the brain appear to be effective in obtaining a specific effect on the afternoon PRL surge; the CMA, suprachiasmatic nuclei, AP, and CC are not estrogen feedback sites for the induction of PRL release, and the MPO was the most sensitive area of the estrogen action in the brain regions examined for the induction of the afternoon PRL surge.

Amygdala↗

PubMed1984

Ovariectomized Sprague-Dawley and Long-Evans rats release prolactin differently in response to estrogen.

Mature female Sprague-Dawley (SD) and Long-Evans (LE) rats were ovariectomized (OVX), fitted with indwelling atrial catheters and given a single sc injection of either 25 or 100 micrograms polyestradiol phosphate (PEP); seven days later blood samples were withdrawn at two hour intervals from 1100 to 2100 hours to detect the presence of an afternoon surge of prolactin (PRL). Other groups of OVX rats of both strains also treated with PEP and catheterized as above were sampled before and at 2, 5, 10 and 30 min after iv administration of 1 microgram synthetic thyrotropin releasing hormone (TRH). Pituitary (AP) and uterine weights were determined following sacrifice one day after TRH treatment. Separate groups of OVX rats of both strains treated with 100 micrograms PEP were decapitated 7 days later and each AP was removed and homogenized. The AP homogenates and plasma samples were assayed for PRL by radioimmunoassay. Rats of both strains had afternoon PRL surges and in both strains the magnitude and/or duration of the surges were enhanced by the higher dose of PEP. However, within each PEP dose LE rats released significantly more PRL during the surge than did SD rats. Rats of both strains also released PRL in response to TRH and this response was enhanced in both strains by the higher of the two doses of PEP. However, there were no differences between the strains at 25 micrograms PEP and at 100 micrograms PEP SD rats released significantly more PRL to TRH than did LE rats. Pituitary weight and PRL concentration were not different between the strains at either dose of PEP but LE rats had significantly heavier uteri at both doses of PEP compared to SD rats. These data not only show that strain differences exist in estrogen-induced or mediated PRL release in the rat but also indicate that the differences are not uniform. This latter observation suggests that the estrogen-induced mechanisms examined in this study are for the most part independent of each other.

Animals↗

PubMed1984

Are both the nocturnal and diurnal prolactin surges necessary to maintain pseudopregnancy in the rat?

Experiments were performed to determine whether both prolactin (PRL) surges are required to maintain pseudopregnancy (PSP) in the rat. Vaginal cycles were followed and animals that exhibited 2-3 normal cycles were cervically stimulated electromechanically to induce PSP. In one set of experiments the afternoon PRL surge was blocked by i.p. injection of 100 micrograms of 2Br-alpha-ergocryptine (CB-154) at 1200 and 1600h while the nocturnal surge was blocked by injecting 100 micrograms of CB-154 at 2400 and 0400h immediately after cervical stimulation. Pseudopregnancy was maintained only in those animals receiving CB-154 injections in the afternoon. In another series of experiments the initial CB-154 injection, given to block either surge, was delayed for one day. Once again only the nocturnal surge was capable of maintaining PSP in all animals. For those animals who had an initial nocturnal surge but all subsequent nocturnal surges were blocked, the afternoon surge was able to support PSP in only 50% of the animals. In those animals whose afternoon PRL surge was blocked, the duration of the nocturnal surge was extended so that it provided 85% of the total PRL produced by control PSP animals. In those animals whose nocturnal surge was blocked, the duration of the afternoon surge was also extended, however, in this case the extended surge only accounted for 58% of the total PRL produced by control PSP animals. The results indicated that when the diurnal PRL surge was blocked the nocturnal surge was extended so that the amount of PRL released was nearly equivalent to the amount released by both surges, however, when the nocturnal surge was blocked the extension of the diurnal surge did not provide adequate PRL to maintain PSP in all animals.

Animals↗

PubMed1984

The effect of steroids on the size heterogeneity of pituitary prolactin in castrate male rats.

Male Sprague-Dawley rats were castrated and given daily sc. injections of estradiol (E2, 10 micrograms/day), testosterone propionate (TP, 1.0 mg/day), dihydrotestosterone (DHT, 1.0 mg/day) or sesame oil (SO, 0.2 ml/day). A group of sham castrate males received daily sc. injections of SO (0.2 ml/day). On day 8 of steroid treatment animals were decapitated and anterior pituitaries were removed and hemisected. Each half was homogenized in PBS buffer (0.01 M Na2HPO4-NaH2PO4; 0.14 M NaCl; 0.1% bovine serum albumin) at either pH 7.6 or 10.6. Homogenates were chromatographed on Sephadex G-100 columns and eluted fractions were assayed for prolactin (PRL) by RIA. Four immunoreactive forms of PRL, designated as "void volume," "big big," "big" and "little," were eluted from the pituitary homogenates of each experimental group. Homogenates obtained at pH 7.6 contained a greater percentage of PRL in the "void volume" and less activity in the "big" and "little" forms than pH 10.6 homogenates in all experimental groups. Pituitaries from SO- and TP-treated castrate animals contained significantly greater percentages of activity in the "void volume" at pH 7.6 compared to the other groups. At pH 10.6, the pituitary homogenates from the E2-treated group eluted a significantly greater percentage of "big" PRL and a smaller percentage of "little" PRL compared to all other groups. These findings suggest that androgenic and estrogenic steroids may play a role in the pituitary PRL molecular size profile of the male rat.

Animals↗

PubMed1984

Prolactin levels and molecular heterogeneity in rat strains with high and low incidence of DMBA-induced mammary tumors.

We compared the following parameters in Long-Evans (LE) and Sprague-Dawley (SD) female rats: 1) mammary tumor incidence after DMBA, 2) plasma prolactin (PRL) during the estrous cycle before and after DMBA, 3) plasma PRL in immature females from 0900 hr on day 29 to 0900 hr on day 30, 4) plasma PRL from 1200 to 1700 hr and before and 10 min after i.p. TRH administration in ovariectomized (OVX) rats treated with 200 micrograms polyestradiol phosphate (PEP), 5) anterior pituitary (AP) PRL concentration in OVX rats treated with 200 micrograms PEP, and 6) levels and Sephadex G-100 gel filtration patterns of plasma PRL 10 min after i.p. TRH administration in OVX rats treated with 200 micrograms PEP. We observed marked mammary tumor incidence in SD rats from one supplier (S-SD, Spartan) (96%) compared to SD from another supplier (CR-SD, Charles River) (40%) or LE rats (10%). Plasma PRL was significantly decreased on metestrus-diestrus and increased on proestrus-estrus in SD (both suppliers) but not in LE rats 90 days after DMBA compared to rats not given DMBA and sacrificed at same stages of the estrous cycle on day 55 of age. Immature LE and SD-CR females exhibited significant late afternoon and early morning prolactin surges on days 29-30 whereas SD-H rats had either no surges or poorly synchronized surges at the same times.(ABSTRACT TRUNCATED AT 250 WORDS)

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1984

Correlation and comparison of Nb2 lymphoma cell bioassay with radioimmunoassay for human prolactin.

Serum samples from groups of men and women with normal and elevated prolactin (PRL) levels were assayed by radioimmunoassay (RIA) and by Nb2 lymphoma cell bioassay (BA) for the presence of PRL. Because the Nb2 lymphoma cells respond to both PRL and growth hormone, BA for PRL activity was carried out before and after neutralization of growth hormone in the serum samples. There were excellent correlations between RIA and BA both in euprolactinemic (r = 0.7587; P less than 0.002) and hyperprolactinemic (r = 0.9558; P less than 0.001) subjects. On an absolute basis, RIA and BA values were similar in the euprolactinemic group (6.6 +/- 0.8 versus 6.2 +/- 1.0), whereas in the hyperprolactinemic group, RIA values were significantly higher than the BA results (89.41 +/- 22.4 versus 62.1 +/- 21.2). The two assay systems also appeared to correlate better in women who were hyperprolactinemic, with obvious menstrual cycle disturbances, than in hyperprolactinemic women without menstrual cycle disturbances.

Biological Assay↗

PubMed1984

Pituitary gonadotropin-releasing hormone (GnRH) receptor responses to GnRH in hypothalamus-lesioned rats: inhibition of responses by hyperprolactinemia and evidence that testosterone and estradiol modulate gonadotropin secretion at postreceptor sites.

Increased hypothalamic GnRH secretion appears to influence positively the number of pituitary GnRH receptors (GnRH-R). GnRH-R increase after castration in male rats, and this rise can be prevented by testosterone (T), anti-GnRH sera, or hypothalamic lesions. GnRH also increases serum LH and GnRH-R in hypothalamus-lesioned rats, and these animals injected with exogenous GnRH are, therefore, a good model in which to study the site of steroid feedback at the pituitary level. Adult male and female rats were gonadectomized, and radiofrequency lesions were placed in the hypothalamus. Males received T implants, and females received estradiol implants at the time of surgery. Empty capsules were placed in the control animals. Beginning 3-5 days later, animals in each group were injected every 8 h with vehicle (BSA) or GnRH (0.002-200 micrograms/day) for 2 days. After these GnRH injections, all rats received 6.6 micrograms GnRH, sc, 1 h before decapitation to determine acute LH and FSH responses. GnRH-R were determined by saturation analysis using 125I-D-Ala6-GnRH ethylamide as ligand. In males, GnRH injections increased GnRH-R. T inhibited acute LH and FSH responses to GnRH in all groups, but had little effect on GnRH-R, indicating that T inhibits gonadotropin secretion at a post-GnRH receptor site. In females, the GnRH-R response to GnRH was less marked, and only the 200 micrograms/day dose of GnRH increased GnRH-R, indicating that the positive feedback effects of estradiol at the pituitary level are also exerted at a site distal to the GnRH receptor. There was no positive correlation between the number of GnRH-R and GnRH-stimulated gonadotropin release in males or females. Female rats with hypothalamic lesions had markedly elevated serum PRL levels (greater than 300 ng/ml). Suppression of PRL secretion by bromocryptine resulted in augmented GnRH-R responses to GnRH, and GnRH-R concentrations rose to the same values induced in males. This suggests that hyperprolactinemia inhibits GnRH-R responses to GnRH in females by a direct action on the pituitary gonadotroph.

Animals↗

PubMed1984

The influence of blinding, olfactory bulbectomy, and pinealectomy on twenty four-hour plasma prolactin levels in normal and neonatally androgenized female rats.

The influence of blinding (BLD), olfactory bulbectomy (ANOS), and pinealectomy (PX) on 24-h plasma PRL levels was examined in normal and neonatally androgenized (NA) female rats. NA pups were treated at 3 days of age with 1.25 mg testosterone propionate. Surgery was performed on both NA and normal animals at 22-25 days of age. At 10 weeks of age, animals were vaginally smeared, and at 15 weeks, they were ovariectomized, injected with 0.5 mg polyestradiol phosphate, and fitted with atrial catheters for blood sampling. At 16 weeks of age, blood samples were taken over a 24-h period. In normal animals, BLD plus ANOS resulted in half of the animals exhibiting a diestrous vaginal smear, while the other half exhibited at least one vaginal estrus during the 7-day period when vaginal smears were obtained. Ovarian, oviductal, and uterine weights for blinded (BLD) plus olfactory bulbectomized (ANOS) animals exhibiting diestrous smears were significantly less than those of BLD plus ANOS animals exhibiting periodic vaginal estrus. Plasma PRL levels were lower in both animal groups compared with those in sham controls, but BLD plus ANOS animals with small ovaries had significantly lower plasma PRL and BLD plus ANOS animals with large ovaries. PX of BLD plus ANOS animals resulted in endocrine organ weights comparable to those in controls and elevated the plasma PRL levels to those observed in BLD plus ANOS animals with large ovaries. The PRL levels in BLD, ANOS, and pinealectomized animals, however, were still below those in sham control animals. Sensory deprived animals had peak PRL values at various times of day, and regrouping of the data from the peak PRL time for each animal suggested the presence of a free-running plasma PRL rhythm. In NA animals, a decrease was also observed in endocrine organ weights and plasma PRL for BLD plus ANOS animals similar to that observed for normal BLD plus ANOS animals. However, all animals in the NA BLD plus ANOS group responded with a constant diestrous smear, small ovaries, and low plasma PRL values. PX prevented the decrease in endocrine organ weights and plasma PRL observed in BLD plus ANOS animals. As in normal animals, NA animals also exhibited a free-running PRL rhythm when sensory deprived.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1983

Effect of estrogen administration on the induction of the plasma prolactin afternoon surge and on anterior pituitary prolactin concentration extracted at different pHs.

Ovariectomized (OVX) rats were injected with various doses of polyestradiol phosphate (PEP); the anterior pituitary (AP) prolactin (PRL) concentration and the plasma afternoon surge of PRL were observed 1 week later by radioimmunoassay. AP PRL was extracted using carbonate and phosphate buffers at either pH 7.6 or 10.6. The AP concentration of PRL was greater when the AP was extracted with buffers at pH 10.6 and the phosphate buffer was the most efficient. The concentration of PRL in the AP more closely reflected the magnitude of the estrogen-induced afternoon surge when the AP was extracted at pH 10.6 and this was especially so when the higher levels of estrogen were administered.

Animals↗

PubMed1983

Influence of blinding, olfactory bulbectomy and pinealectomy on plasma prolactin levels in the neonatally androgenized female rat.

Female rats were neonatally androgenized (NA) by administering 1.25 mg of testosterone propionate at 3 days of age. At 21-23 days of age, groups of 12 animals each were blinded (BLD), olfactory bulbectomized (ANOS) and pinealectomized (PX) either alone or in combination. At 11 weeks of age all animals were ovariectomized, implanted with atrial catheters and given 0.5 mg polyestradiol phosphate. At 12 weeks of age, animals were attached to catheter extensions and blood samples obtained at 09.00, 11.00, 13.00, 15.00, 17.00, 19.00 and 21.00 h. The plasma prolactin (PRL) pattern of NA control animals consisted of elevated basal values at 11.00 and 13.00 h with an afternoon peak at 17.00 h. Anosmic and PX animals had a PRL pattern similar to that of the control. Animals BLD or BLD + ANOS had significantly lower plasma PRL values than sham-operated animals. Animals BLD + PX had PRL values comparable to PX alone. The diurnal PRL pattern observed for NA control animals was still evident in all experimental animals. Blinding + ANOS resulted in a significant decrease in ovarian and oviductal weights and attenuated the estrogen-induced increase in uterine weight. The evidence indicated that the elevated morning PRL levels observed in NA rats was not due to an altered function of the pineal gland and that BLD + ANOS blunted the action of exogenous estrogen on uterine weight.

Aging↗

PubMed1983

Inhibition of suckling-induced prolactin release by estrogen in ovariectomized lactating rats: bioassay versus radioimmunoassay.

Plasma levels of prolactin (PRL) were determined before and during suckling in intact and ovariectomized (OVX) lactating rats treated 5 days earlier with a single sc injection of 50 micrograms polyestradiol phosphate (PEP) or saline. Radioimmunoassay (RIA) and the Nb2 lymphoma cell bioassay (BA) were used to measure plasma PRL. Pituitary PRL concentrations were also determined by the two assays. In addition, lactational performance was estimated by measuring litter weight gain before and after estrogen treatment. Lactation was inhibited by PEP in intact rats; however, PEP did not alter plasma or pituitary levels of PRL in this group. Lactation was not inhibited by estrogen in OVX rats, but plasma PRL levels were significantly reduced at 10, 30, and 45 min of suckling. In addition, there was no evidence of an estrogen-induced afternoon prolactin surge in either PEP-treated group. The lactational inhibition in the intact, PEP-treated rats was probably due to combined effects of estrogen and progesterone. Plasma progesterone concentration was 64 +/- 8 ng/ml in the intact PEP-treated group compared to 3 +/- 1 ng/ml in the OVX, PEP-treated rats. The exact mechanism for the supression or delay in suckling-induced plasma PRL in the OVX, PEP-treated females remains unresolved but it was not due to an increase in suckling-induced corticosterone levels. The qualitative changes in plasma PRL during suckling in the various groups detected by RIA were also detected by the BA. However, there were slight quantitative differences between the two assays. When plasma PRL was low (nonsuckled states) the BA/RIA ratio was less than that observed when the plasma PRL was high (during suckling), i.e., more bioactive PRL was apparently released by suckling. However, these differences between RIA and BA may have been due in part to the fact that very low or very high levels of prolactin approached the minimal and maximal assay limits of the RIA but not the BA indicating that care be exercised when making such assay comparisons.

Animals↗

PubMed1982

Rat lymphoma cell bioassay for prolactin: observations on its use and comparison with radioimmunoassay.

The rat Nb2 node lymphoma cell bioassay (BA) for prolactin (PRL) was validated for use in our laboratories. During the course of this validation we observed that rat prolactin (NIAMDD-RP-1) stimulated cell division by as much as 16.5 fold over the range of 0.04 to 40.0 ng/ml at the end of 72 hours of incubation. We also observed a dose related increase in the size of the lymphoma cells. Prolactin concentrations in rat plasma, serum, anterior pituitary (AP) homogenates and milk were measured by both radioimmunoassay (RIA) and BA. In individual BA's there was parallelism between samples and standard; but when several dilutions of the same plasma and pituitary homogenates were assayed repeatedly, higher PRL levels were consistently observed for the more concentrated samples. At low or moderate levels of plasma PRL there was excellent agreement between RIA and BA; however, at high levels plasma PRL bioactivity exceeded radioimmunoactivity by a small, but significant, amount. A comparison of pituitary PRL concentrations measured by RIA and BA were in good agreement when homogenization was done at pH 10.6. However, when homogenization was done at pH 7.6, slightly but significantly more PRL was extracted when assayed by BA than when assayed by RIA.

Animals↗

PubMed1982

Stress-induced decrease of the afternoon prolactin surge. The influence of the adrenal gland.

Blood sampling initiated during the afternoon in ovariectomized, estrogen-treated rats resulted in a suppression of the prolactin (PRL) surge. The administration of 2.5 micrograms or 25 micrograms of corticosterone (B) immediately after the first blood sample did not alter the course of the PRL suppression. Plasma B levels of adrenal intact controls were not acutely altered by blood sampling and the normal afternoon increase was evident. Similar treatment of adrenalectomized rats resulted in a similar pattern of PRL suppression. The data indicated that adrenal secretions were not responsible for the decrease in plasma PRL induced by blood sampling initiated in the afternoon.

Adrenal Glands↗

PubMed1982

The influence of testosterone administration on plasma prolactin levels in the neonatally androgenized (NA) female rat.

Neonatally androgenized (NA) female rats were ovariectomized (OVX) as adults and given 1 mg of testosterone propionate/day for 7 days and the plasma prolactin (PRL) pattern compared with NA intact animals and normal OVX animals given estrogen or TP. NA intact animals had elevated basal (morning values) and an attenuated afternoon surge when compared to normal estrogen-treated animals. Testosterone administration to normal animals induced an afternoon surge similar to that of normal estrogen-treated animals but the magnitude of the surge was less. Testosterone given to NA-OVX animals had little effect on either morning or afternoon PRL levels. The results suggest that in the NA rat the brain region involved in the conversion of testosterone to estrogen may be altered by neonatal androgen exposure.

Aging↗

PubMed1982