Significant qualitative differences exist between thyrotropin and prolactin secretory dynamics induced by pituitary cell swelling

Cell swelling produced by a variety of techniques is a potent stimulus intensity-related inducer of an immediate secretory burst of thyroid-stimulating hormone (TSH) and prolaction (PRL) secretion from anterior pituitary cells. A 2-min "square wave" exposure to either hyposmolarity or isotonic urea induced stimulus intensity-correlated TSH and PRL secretory bursts peaking within 3 min, but the PRL zenith occurred 1 min later than that of TSH. With continuous exposure to these stimuli, TSH secretion rapidly decreased and remained only slightly above the unstimulated rate after 5 min. PRL secretion fell to and remained below the unstimulated level after 10 min. After stopping the stimulus, another secretory burst ("off" response) occurred with PRL, but not with TSH. A progressive "ramp" increase in stimulus intensity over 18 min induced a corresponding gradual increase in TSH secretion; there was a progressive depression, rather than increase, in PRL secretion during the stimulus ramp, with an off response secretory burst when the stimulus was discontinued. Removal of extracellular Ca2+ or addition of verapamil to the medium did not alter the dynamics of hyposmolarity-induced TSH secretion, but markedly altered those of PRL secretion; there was no off response PRL secretion and a hyposmolar ramp induced a corresponding gradual increase in PRL secretion, with a return to baseline after removing the stimulus. The dramatic qualitative differences in the response of the thyrotroph and lactotroph may reflect differences between the cell types in the size of secretory vesicles, membrane potential, the mechanism of exocytosis, and/or the role of Ca2+ influx across the plasmalemma.     

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.     

Identification by immunofluorescence of various categories of anterior pituitary gland cells (somatotropin, prolactin, corticotropin, melanotropin, gonadotropin, and thyrotropin cells) in the spermophile (Citellus variegatus)]

Using antibodies against human STH, rat prolactin, 1-24, 17-39-synthetic ACTH, alpha- and beta-synthetic MSH, ovine LH, porcine LH beta, bovine TSH saturated with LH, it is possible to identify somatotropic, prolactin, corticotropic, melanotropic, gonadotropic and thyreotropic cells in the adenohypophysis of rodents Citellus variegatus and Graphiurus murinus. The topographical repartition and morphological characters of these cells are described.     

Alkalin titrations of human somatotropin, human choriomammotropin and ovine prolactin by circular dichroism and fluorescence.

Structural transitions occurring during the alkalin titration of human somatotropin, human choriomammotropin, and ovine prolactin have been investigated by means of circular dichroism and fluorescence emission spectra. Human somatotropin exhibited an isodichroic point at 287 nm, with all spectral changes being reversed upon back titration from pH 12.50 to pH 8.0. Fluorescence quenching as a function of pH produced a simple sigmoidal curve. Human choriomammotropin exhibited an isodichroic point at 288 nm. The fluorescence and circular dichroism spectra of this protein were found to be reversible between pH 8.0 and 11.0. However, on titration above pH 11, the isodichroic point and the reversibility of the circular dichroism spectra were lost. This conformational transition was accompanied by a sharp increase in fluorescence quantum yield. The circular dichroism spectra of ovine prolactin showed essentially no change on titration to pH 11.0. However, between pH 11.0 and 12.0, a sharp conformational transition was observed similar to that seen in human choriomammotropin, but not exhibiting the same increase in fluorescence quantum yield. The fluorescence titration of prolactin was found to be essentially reversible upon back titration from pH 12.5, although the circular dichroism spectra were not reversible from this pH.     

Changes in prolactin and testosterone levels induced by acute physical exertion in young female athletes

In order to establish the influence of acute atypical exercise on prolactin and testosterone levels in young female athletes the authors selected a group of 13 short distance runners who were subjected to exercise on a cycle ergometer. Hormone levels were measured before the test, just after the end of test, 30 and 90 minutes thereafter. Significant increase in testosterone concentration appeared immediately after the exercise and 90 minutes after completion of a test testosterone level returned to preexercise levels. Unlike the results of other authors statistically significant decrease in plasma prolactin concentration was found 90 minutes after the end of test.     

Effects of repeated whole-body cold exposures on serum concentrations of growth hormone, thyrotropin, prolactin and thyroid hormones in healthy women

Cold therapy is used to relieve pain and inflammatory symptoms. Humoral changes may account for the pain alleviation related to the cold exposures. The aim of the present study was to examine the effects of two types of cold therapy, winter swimming in ice-cold water (WS) and whole body cryotherapy (WBC), on the serum levels of the growth hormone, prolactin, thyrotropin and free fractions of thyroid hormones (fT3, fT4). One group of healthy females (n = 6) was exposed to WS (water 0–2 °C) for 20 s and another group (n = 6) to WBC (air −110 °C) for 2 min, three times a week for 12 weeks. Blood samples used for the hormone measurements were taken on weeks 1, 4 and 12 before and 35 min after the cold exposures and on the days of the respective weeks, when the cold exposures were not performed. During the WS treatments, serum thyrotropin increased significantly at 35 min on weeks 1 (p < 0.01) and 4 (p < 0.05), but the responses were within the health-related reference interval. During the WS, the serum prolactin measured at 35 min on week 12 was lower than during the control treatment, and no changes in fT3 or fT4 were observed. During the WBC, no changes in the serum levels of the studied hormones were observed during the 12 weeks. In conclusion, repeated WS and WBC treatments for healthy females do not lead to disorders related to altered secretions of the growth hormone, prolactin, thyrotropin, or thyroid hormones.     

Effect of fenfluramine on growth hormone and prolactin secretion in obese subjects

Obese subjects show a subnormal growth hormone (GH) and prolactin (PRL) release in response to a variety of stimuli. Fenfluramine, an anorexiant drug used in obesity therapy, may have some effects on hypothalamic-pituitary function mediated by serotoninergic stimulation. The present investigation in obese subjects was carried out to study the effects of fenfluramine (60 mg orally) on GH and PRL secretion after intravenous arginine infusion. Ten volunteer obese females were studied and compared with 10 volunteer normal weight controls. In the obese group the GH response to arginine was significantly lower than in control group. Fenfluramine administration restored the subnormal GH response to arginine in obese subjects. The PRL response to arginine in obese women was subnormal. Fenfluramine administration restored the response of PRL to arginine infusion to normal. In conclusion, fenfluramine--under acute circumstances--enhances the hypothalamic-pituitary response to arginine in obese subjects. The decreased GH and PRL output in obese subjects is not due to an absolute hormonal deficiency and this effect of fenfluramine on GH secretion may--due to its lipolysis stimulation--be useful in obesity treatment.     

Concentrations of somatotropin and prolactin in the follicular fluid and blood serum of cows in different phases of the estrous cycle

Comparative investigations of somatotropin and prolactin contents in the fluid of antral follicles and blood serum of cows in different phases of the oestrous cycle were performed. The somatotropin concentration in the fluid was shown to rise with increasing the follicle diameters from 3-5 to 6-10 mm in the follicular phase and to decrease in follicles of diameter 11-20 mm in the luteal phase. The prolactin concentration was higher in the fluid of follicles 11-20 mm in diameter than in those of 3-5 mm in diameter in the follicular phase and did not depend on the follicle size in the luteal phase. Concurrently, the prolactin content in follicles 3-5 mm in diameter was higher in the luteal than follicular phase of the cycle. As compared to the follicular phase, an increase in the prolactin concentration in the bovine blood serum during the luteal phase was also found. The data obtained indicate that changes in the somatotropin and prolactin contents in the follicular fluid are related to processes regulating growth and development of antral follicles depending on the phase of oestrous cycle and to changes in the blood hormone concentrations as well.     

Dissociation of thyrotropin and prolactin responsiveness to thyrotropin releasing hormone stimulation in L-dopa treated parkinsonian patients

The hPRL, hTSH and T3 response to thyrotropin releasing hormone (TRH) stimulation (200 microgram i.v.) were studied in 8 parkinsonian patients under chronic L-dopa-carbidopa therapy. In 6 out of the 8 patients studied, treatment was stopped for a period of 2 weeks and the TRH stimulation test was repeated under similar experimental conditions. In the L-dopa-carbidopa treated patients basal hTSH levels and the hTSH response to TRH were significantly suppressed. By contrast, in the 6 patients 2 weeks after cessation of treatment, although basal hTSH levels were still suppressed, a normal hTSH response to TRH was observed. Neither the basal T3 and T4 concentrations, nor the T3 response to TRH were affected by the L-dopa-carbidopa treatment. In addition, basal hPRL levels as well as the hPRL: response to TRH were within the normal range in the two groups of patients studied. Our study provides further support for a dopaminergic inhibitory action on the hypothalamo-hypophyseal-thyroidal axis (HHTA). The inhibition of basal hTSH secretion and th hTSH response to TRH by L-dopa, suggest that the blocking action of dopamine is exerted at the hypothalamic as well as at the pituitary level. In our hands, chronic administration of L-dopa did not affect either tonic hPRL secretion of the hPRL response to TRH. The dissociation or response to TRH under the same inhibitory action of dopaminergic stimulation can be interpreted as demonstrating a greater sensitivity of the pituitary thyrotrophs, than the prolactin secreting cells, to the blocking effect of dopamine.     

Cell swelling induced by the permeant molecules urea or glycerol induces immediate high amplitude thyrotropin and prolactin secretion by perifused adenohypophyseal cells

The permeant molecules, urea and glycerol, evoked a prompt secretory burst of TSH and PRL when added to the extracellular medium of acutely dispersed anterior pituitary cells. Secretion of both hormones was proportional to the concentration of urea or glycerol between 26 and 104 mM (r greater than 0.89, P less than 0.001). Equivalent concentrations of the impermeant molecule, mannitol, did not induce secretion. The acute TSH and PRL secretory responses to TRH, hyposmolarity, and permeant molecules were qualitatively indistinguishable. These data support our hypothesis that cell swelling and resultant plasmalemma expansion is a potent inducer of hormone secretion. Since the secretory response to permeant molecules was not reduced in a Ca2+-free medium containing 0.1 mM EGTA, an increase in Ca2+ transport across the plasmalemma to raise cytosol Ca2+ concentration does not appear involved.