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

A Century of Prolactin: Emerging Perspectives as a Metabolic Regulator

Prolactin, a hormone that has been studied for almost a century, has evolved from a reproductive regulator to a key player in metabolic health. Initially identified for its lactogenic role, the impact of prolactin on glucose and lipid metabolism became evident in the 1970s, leading to a paradigm shift in our understanding. Deviations in prolactin levels, including hyperprolactinaemia and hypoprolactinaemia, have been associated with adverse effects on glucose and lipid metabolism. Mechanistically, prolactin regulates metabolic homoeostasis by maintaining islet abundance, regulating the hypothalamic energy regulatory centre, balancing adipose tissue expansion, and regulating hepatic metabolism. Given the widespread use of pharmaceutical agents that affect prolactin levels, it is important to examine prolactin-related metabolic effects. Recently, a profound exploration of the intricate metabolic role of prolactin has been conducted, encompassing its rhythm-dependent regulatory influence on metabolism and its correlation with cognitive impairment associated with metabolic diseases. In this review, we highlight the role of prolactin as a metabolic regulator, summarise its metabolic effects, and discuss topics related to the association between prolactin and metabolic comorbidities.

The influence of other than prolactin hormones on bone mineral density in women with hyperprolactinaemia of various origins

OBJECTIVE

Hyperprolactinaemia may lead to bone loss, both due to hypogonadism and other hormonal disturbances. Aim of the case-control study was the analysis of influences of hormonal profiles associated with hyperprolactinaemia on the bone mineral density (BMD) in women with hyperprolactinaemia of various origin.

MATERIAL AND METHODS

The subjects were 32 patients with prolactinoma, 43 ones with functional hyperprolactinaemia and 29 healthy controls. All of them were studied for BMD (lumbar spine, proximal femur, forearm, total body) by dual-energy X-ray absorptiometry and their correlations with hormones levels (prolactin, oestradiol, luteinising hormone, follicle stimulating hormone, sex hormone binding globulin (SHBG), testosterone, dehydroepiandrosterone sulphate (DHEA-S), insulin-like growth factor-1 and intact parathyroid hormone) using Spearman correlation analysis and multiple regression analysis model.

RESULTS

Correlation analysis revealed the anabolic influence of PTH on lumbar spine in women with prolactinoma, and on ultradistal radius in functional hyperprolactinaemia. In multiple regression analysis, oestradiol had greatest influence on lumbar spine and total body BMD. Moreover, positive influence of testosterone, SHBG on spine BMD, and of oestradiol, testosterone, SHBG and DHEA-S on total body BMD were observed in patients with prolactinoma.

CONCLUSION

Hormonal disturbances associated with hyperprolactinaemia influence BMD more in patients with prolactinoma than in ones with functional hyperprolactinaemia.

Hypercalciuria in hyperprolactinemic rats: effects of benzthiazide

There is evidence that prolactin (PRL) excess plays a role in the etiology of osteoporosis associated with human prolactinoma. Calcium balance in human hyperprolactinemia has not been thoroughly investigated. In the present study, rats with excess circulating PRL levels (male anterior pituitary-grafted Fischer 344 rats) had urinary calcium excretion twice that of control rats (4.16 +/- 0.43 v 2.25 +/- 0.30 mg/24h X 100 g BW). Calcium excretion expressed per mg of calcium intake was also high in pituitary-grafted rats. The excess calcium excretion in hyperprolactinemic rats was not accompanied by a concomitant rise in sodium excretion. This dissociation suggests that PRL has an effect on the renal handling of calcium. Since thiazide diuretics have a well-described hypocalciuric action, their effect was tested in these rats. In normal rats, benzthiazide, a long-acting agent, significantly reduced urinary calcium excretion in a dose-dependent fashion. Hyperprolactinemic rats responded to benzthiazide in a manner similar to control rats. In pituitary-grafted rats, benzthiazide also decreased the calcium excretion to intake ratio and normalized the calcium to sodium excretion ratio. Since the hypercalciuria of experimental hyperprolactinemia can be corrected by thiazide diuretics, these agents may have therapeutic potential in human PRL excess.