Effects of parathyroid hormone infusion and primary hyperparathyroidism on serum prolactin in man

[Prolactinomas and bone mineral density in men]

Throughout the years evidence has been accumulated on the morbidity of hyperprolactinemia, particularly in terms of bone mineral density decrease. This complication of hyperprolactinemia affects both women and men. In this paper, we analyze aspects related to bone loss in men with hyperprolactinemia due to prolactinomas: prevalence, clinical relevance, physiopathology, diagnosis and the consequences of the treatment of hyperprolactinemia and hypogonadism on bone mineral density.

Parathyroid hormone-induced dopamine turnover in the rat medial basal hypothalamus

The parathyroid hormone (PTH) gene is expressed and translated in the rat hypothalamus, and the possibility that PTH may modulate neural activity was therefore examined in anesthetized rats. Intracerebroventricular (ICV) injections of 1.0 or 10.0 micrograms rat, human, or bovine PTH(1-34) was followed 60 min later by increased concentrations of DOPAC (dihydroxyacetic acid) and the DOPAC:dopamine (DA) ratio in the medial basal hypothalamus (MBH), but not in other (brainstem, cerebral cortex, cerebellum) regions of the brain. Tissue concentrations of norepinephrine and serotonin were unchanged by ICV PTH administration, although MBH concentrations of 5-hydroxyindolacetic acid (5-HIAA) were increased following PTH administration. An increase in MBH DA turnover (as indicated by an increased DOPAC:DA ratio) was also induced by the ICV injection of 10 micrograms PTH-related protein [PTHrP(1-34)]. Pretreatment with the receptor antagonists PTH(7-34) or PTHrP(7-34) completely blocked the subsequent DOPAC response to ICV PTH or PTHrP, respectively. The DOPAC concentrations in hypothalamic extracellular fluid (ECF), sampled by microdialysis, were also increased within 20 min of PTH(1-34) perfusion, in the absence of changes in the ECF concentrations of 5-HIAA. These results demonstrate that PTH and PTH-like peptides specifically increase DA turnover in the rat MBH and suggest novel roles for these hormones in neural regulation.

Dopaminergic actions of parathyroid hormone in the rat medial basal hypothalamus in vitro

Parathyroid hormone (PTH) modulates dopamine (DA) metabolism in the rat medial basal hypothalamus (MBH) in vivo. Direct effects of PTH on MBH DA metabolism were therefore investigated in vitro. Incubation of rat MBHs for 60 min with 10(-7)-10(-5) M human PTH1-34 consistently reduced the tissue DA content and increased the DOPAC (dihydroxyphenylacetic acid) to DA ratio. This ratio was further increased in tissues incubated in 10(-5) M PTH1-34, as a result of an increase in DOPAC content. The tissue content of DOPAC and DA was unaffected by 10(-9) M PTH. The serotonin (5HT) content of the MBH was reduced by 10(-5) M PTH1-34, but concentrations of 5HT, 5-hydroxyindolacetic acid, and norepinephrine were otherwise unaffected by 10(-9)-10(-5) M PTH1-34. Concentrations of DA in the incubation media were reduced after exposure to 10(-6) or 10(-5) M PTH1-34. The uptake of 3H-labelled DA by incubated tissues was also reduced by 10(-6) M PTH1-34, as was the metabolism of 3H-labelled DA into tissue and media DOPAC. Monoamine oxidase (MAO) activities A and B were significantly increased after the incubation of the MBH with 10(-6) or 10(-5) M PTH1-34. These results further demonstrate neuromodulatory actions of PTH on dopaminergic neurons within the rat MBH in vitro, and suggest neural and/or neuroendocrine roles of PTH of central or peripheral origin.

Drug-induced changes in prolactin secretion. Clinical implications

Prolactin secretion is affected by various diseases as well as by many drugs in humans and animals. While marked hyperprolactinaemia suggests the presence of a pituitary tumor, moderate changes may also occur in various endocrine or non-endocrine disorders. Drugs can interfere with prolactin regulation via complex mechanisms at the hypothalamus or at the pituitary site, but possible changes in prolactin metabolism are poorly understood as yet. This survey of the literature up to June 1986 covers the influence of various groups of drugs and agents on the plasma prolactin level under various conditions. It contains information that will facilitate evaluation of whether hyper- or hypoprolactinaemia may result from therapeutic intervention or must be related to an underlying disease. It is obvious that more subtle changes can be revealed by the use of dynamic tests either to stimulate or to suppress prolactin secretion.

Melatonin, cortisol, prolactin, and calcitonin secretion in primary hyperparathyroidism before and after surgery

The aim of the present study was to determine the diurnal secretion of melatonin, cortisol, prolactin, and calcitonin during chronic parathyroid hormone-dependent hypercalcemia. Eight women, aged 40-76 years, with primary hyperparathyroidism (PHPT) were studied before and after surgical removal of a parathyroid adenoma. The hormone concentrations in blood were determined at 08, 12, 16, 22, 02, 04, and 06 h. Concomitantly, the excretion of melatonin and cortisol in urine between 07-19 h and 19-07 h, and the clearance of calcium and creatinine were measured. Nyctohemeral serum prolactin and calcitonin were unaffected by moderate parathyroid hormone-dependent hypercalcemia. In contrast, serum cortisol and melatonin were significantly higher during active disease than after surgical cure. Mean 24-h variation of serum cortisol was 349 +/- 34 nmol/liter vs. 223 +/- 17 nmol/liter and mean serum melatonin was 0.13 +/- 0.04 nmol/liter vs. 0.06 +/- 0.02 nmol/liter. Endogenous creatinine clearance was similar before and after surgery, while the clearance of melatonin and cortisol significantly increased after surgery, indicating an increased tubular reabsorption of both hormones during active disease. Fasting morning glucose concentrations were also significantly decreased after successful surgery, 6.1 +/- 0.6 vs. 5.2 +/- 0.5 mmol/liter. It is suggested that the relative hypercortisolism may be the cause of the glucose intolerance in primary hyperparathyroidism. Three to 4 months after surgical cure the serum melatonin levels were significantly lower than those seen in age-matched controls, indicating a melatonin insufficiency in patients successfully treated for PHPT. The meaning of this finding is not yet understood but might be of importance in the development of primary hyperparathyroidism.

Increased forearm bone mineral content after bromocriptine treatment in hyperprolactinemia

We studied 15 hyperprolactinemic women to evaluate possible modifications of bone mineral content after pharmacological treatment. Patients received a dopamine agonist (bromocriptine) for six months after which there was a significant decrease of prolactin plasma levels (P less than 0.01) and a significant increase of bone mineral content (P less than 0.05).

Prolactin and calcium metabolism: influence of hyperprolactinemia on immunoreactive parathyroid hormone levels in man and in the rat

Serum prolactin, parathyroid hormone, P and Ca serum levels were measured in 15 patients (12 women and 3 men) with hyperprolactinemia, and in 6 normal male volunteers who underwent a TRH test (100 micrograms by rapid iv injection) in order to obtain a short-term pharmacologically-induced hyperprolactinemia. A pituitary gland graft under the kidney capsule was carried out on 26 Sprague-Dawley male rats, which became hyperprolactinemic since the transplanted pituitary was stripped of the inhibitory hypothalamic control. Another group of 10 rats was injected with L-sulpiride (0.1 mg/kg). The serum PTH levels in patients and in subjects with induced hyperprolactinemia were within the normal range and there was no correlation between serum PRL and PTH levels. The same occurred both in transplanted and L-sulpiride injected rats. Our results suggest that prolactin does not modify PTH secretion in vivo and therefore, in contrast with previous data, it should not be considered a physiologically relevant secretagogue for parathyroid hormone.