Plasma prolactin secretion

DA antagonists are anti-emetic, elevate plasma prolactin and have major motor and behavioural effects. Thus DA must be involved in the initiation of vomiting, the secretion of prolactin and control of motor and behavioural activity. Its role in emesis and as the prolactin release inhibitory factor have been adequately covered above. Its motor and behavioural function will now be considered. 

Prolactin secretion, at least in experimental animals, is increased following chronic lithium treatment, probably as a consequence of the enhanced sensitivity of posts)maptic 5-HT receptors and the decreased sensitivity of dopamine receptors. In patients on therapeutic doses of the drug, however, the plasma prolactin levels would not appear to be markedly altered. There is little evidence that circulating gonadotrophin concentrations are affected by therapeutic doses of lithium. 

Administration of estrogens is well known to cause an increase in plasma prolactin (PRL) levels in man (43, 44) as well as in the rat (45-48). This stimulatory effect of estrogens is also observed in vitro in anterior pituitary gland explants (49), tumoral adenohypophysial cells (50) and normal rat anterior pituitary cells in primary culture (39, 40, 42, 51). Seventeen-g-estradiol (E2) does not only stimulate basal and TRH-induced PRL secretion in rat anterior pituitary cells in culture but it can also reverse almost completely the inhibitory effect of dopamine (DA) agonists on PRL release (40). 

Introduced by Komfeld and coworkers in 1979 as a dopaminergic agonist that also decreases plasma prolactin concentration, this compound, 230, shows activity in the treatment of acute myocardial infarction with diastolic hypertension. It is also effective in the treatment of pituitary tumors secreting prolactin or growth hormone 102). Its clinicai study revealed its effectiveness in Parkinson s disease, and it is now used clinically. This compound, 230,... 

Figure 7.9 Effects of MDMA pretreatment on secretion of corticosterone (left panel) and prolactin (right panel) evoked by acute MDMA challenge. Male rats received three i.p. injections of 1.5 or 7.5 mg/kg MDMA, one dose every 2 h. Saline was administered on the same schedule. Then 2 weeks later rats received i.v. injections of 1 and 3 mg/kg MDMA. Blood samples were drawn via indwelling catheters plasma corticosterone and prolactin were measured by RIA.126 Data are mean SEM, expressed as ng/ml of plasma for N = 8 rats/group. Baseline corticosterone and prolactin levels were 73 18 and 2.4 0.6 ng/ml of plasma, respectively. Significant compared to saline-pretreated control group (P < 0.05 Duncan s).

It is a peptide containing 14 amino acids and inhibits the release of growth hormone, TSH and prolactin from the pituitary and insulin and glucagon in pancreas. It has a very short plasma half-life. Because of its shorter duration of action and lack of specificity in inhibiting only GH secretion, its use in the treatment of acromegaly is limited. 

Pituitary activity is absolutely central to osmoregulation, and hypophy-sectomy destroys the ability of fish to adapt to a change in salinity. The prolactin is synthesized in, and is secreted by, the pituitary, which also secretes adrenocorticotrophic hormone (ACTH), which, in turn, stimulates the adrenals to produce cortisol. The level of ACTH in the plasma is therefore raised when fish are in sea water (Nichols and Fleming, 1990). The pituitary also secretes growth hormone into the blood plasma in sea water (Yada and Hirano, 1992 rainbow trout) but its role is not clear in the present context. 

Strenuous exercise for 10 minutes increases plasma renin activity by 400%. Cortisol secretion is stimulated and the normal diurnal variation may be abolished. Urinary free cortisol excretion and the plasma concentrations of cortisol, aldosterone, growth hormone, somatotropin, and prolactin are also increased by exercise. Plasma insulin concentration is decreased by exercise. Strenuous exercise increases both the plasma and urinary concentrations of catecholamines. The changes in hormone concentrations are probably responsible for the increase in leukocyte count to about 25,000 cells/juL that has been observed following strenuous exercise. 

There is no circadian variation in the plasma concentrations of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in men, but a 20% to 40% increase of plasma testosterone occurs during the night. Prolactin is secreted, like other hormones, in multiple bursts prolactin concentration is greatest during sleep. 

Physical and mental stress influence the concentrations of many plasma constituents. Anxiety stimulates increased secretion of aldosterone, angiotensin, catecholamines, cortisol, prolactin, renin, somatotropin, TSH, and vasopressin. Plasma concentrations of albumin, cholesterol, fibrinogen, glucose, insulin, and lactate also increase. 

The administration of ji agonists increases the concentration of prolactin in plasma, probably by reducing the dopaminergic inhibition of its secretion. The administration of morphine or P-endorphin has little effect on the concentration of growth hormone in plasma. With chronic administration, tolerance develops to the effects of morphine on hypothalamic releasing factors. Patients maintained on methadone reflect this phenomenon in women, menstrual cycles that had been disrupted by intermittent use of heroin return to normal in men, circulating concentrations of LH and testosterone return to the normal range. 

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