Differences in nocturnal basal and rhythmic prolactin secretion in untreated compared to treated HIV‐infected men are associated with CD4+ T‐lymphocytes
Adalberto ParraGustavo Reyes‐TeránJorge Ramírez‐PeredoBénédicte JacqueminVerónica QuirozMario CárdenasMaria Cecilia García-SanchoFernando Larrea
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Abstract:
The existence of decreased hypothalamic dopaminergic tone in HIV‐infected men has been suggested. In a cross‐sectional study, we determined 12 h nocturnal basal and pulsatile prolactin (PRL) release levels (by blood sampling every 10 min) and their correlation with CD4+ T cells in seven volunteer HIV‐negative, healthy men (group 1), and 21 normoprolactinemic, euthyroid, HIV‐infected men divided into 3 groups (each group = 7): (i) group 2, asymptomatic HIV‐infected stage A1 men, untreated; (ii) group 3, AIDS stage C3 without active opportunistic infections, untreated; and (iii) group 4, previously stage C3 after at least 6 months of successful highly active antiretroviral therapy. Serum PRL was measured by radioimmunoanalysis and the results were analysed by waveform‐independent deconvolution analysis. CD4+ T lymphocytes were measured by flow cytometry and viral load by a nucleic acid sequence‐based amplification assay. No differences were detected in the first two groups. In the third group, however, 100% of prolactin secretion was found to be pulsatile with a shorter secretory burst duration ( P = 0.04), and a greater circulating half‐life and pulse amplitude ( P ≤ 0.04). Group 4 had the greatest basal prolactin secretion ( P ≤ 0.04), and a shorter secretory burst duration ( P = 0.04 vs group 2), circulating half‐life ( P = 0.01 vs group 3) and intersecretory burst interval ( P = 0.06 vs group 1). PRL approximate entropy was similar among all groups. Linear correlations existed between CD4+ T cell counts and PRL secretory burst half duration ( r = 0.62, P = 0.002) and amplitude ( r = −0.63, P = 0.001), and in circulating serum half‐life ( r = − 0.61, P = 0.002) in HIV‐infected groups. Viral load showed no correlations. It is suggested that differential changes in nocturnal prolactin secretion among HIV‐infected men occurred while maintaining the normal coordinate feedback and/or feedforward control within the lactotropic axis. These changes may represent an adaptative mechanism to sustain, by different means, the maximal physiologic PRL production to stimulate the highest cellular immune response and/or reconstitution in attempting to survive.Keywords:
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Pituitary prolactin has been quantified by radioimmunoassay in whole milk obtained from cattle, goats, sheep and rats. Prolactin concentrations in milk samples obtained following the completion of lactogenesis approximate concentrations of the hormone in blood plasma or serum. However, concentrations of prolactin in prepartum mammary secretions were much higher than plasma prolactin in prepartum dairy cows. This observation was consistent with the hypothesis that during mammary lactogenesis, endogenous milk prolactin in the alveolar lumen may be an additional source of biologically active prolactin. The value of milk prolactin to neonatal animals remains unknown. Experiments with milk-fed calves and suckling rats failed to demonstrate absorption of the intact molecule into the neonate's blood. Further research is needed to determine the role, if any, that maternal prolactin consumed in milk plays in neonatal physiology. Measurements of milk prolactin seem to be highly predictive of the average blood prolactin concentration. Milk prolactin can probably be used in lactating females to predict average plasma prolactin in a manner that is relatively independent of stress- or milking-induced increases in pituitary release of the hormone.
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Basal serum prolactin concentrations have been measured in 50 normal prepubertal children. There was no significant difference in prolactin levels between males and females and all concentrations were within the normal range for adult females (3-15 mug/l). Prolactin concentrations before and during insulin hypoglycaemia and intravenous thyrotrophin releasing hormone (TRH) have been measured in normal children of short stature, in children with isolated growth hormone (GH) deficiency and in those with hypothalamo-pituitary disease. There was no difference in either basal or stimulated prolactin levels in the normal group compared with the isolated GH-deficient group. In most of the children with hypothalamo-pituitary disease basal prolactin concentrations were within the normal range but there was an impaired response to both hypoglycaemia and TRH. Basal and stimulated levels of prolactin are compared in the same subjects with those of GH, thyroid stimulating hormone and the gonadotrophins and the clinical value of the dynamic tests described is discussed.
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Abstract Prolactin response to suckling was studied in a group of fully breast feeding women ( N = 58) between 4–6 weeks postpartum. Basal, suckling stimulated and the increment of prolactin showed wide individual variations. Basal prolactin concentrations varied from 140 to 4,600 mlU/ l , suckling stimulated prolactin from 400 to 5,600 mlU/ l and the increment of prolactin from 40 to 4,160 mlU/ l . Basal (p = 0.0395) and suckling stimulated (p = 0.0423) prolactin concentrations significantly increased as the number of night breast feeds increased and the suckling stimulated (p = 0.0218) prolactin concentrations significantly increased as the number of breast feeds/24 h increased. However, the magnitude of the rise in prolactin in response to suckling was not dependent on basal prolactin concentration. Basal, suckling stimulated or the increment of prolactin were not significantly different between subjects having different breast feeding frequencies, when the subjects were grouped according to the number of breast feeds. These differences may be due to the large individual variation in prolactin concentrations seen in women having similar breast feeding frequencies which may arise from individual variations in hypotha‐lamic — pituitary response to suckling.
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During pseudopregnancy in the rat prolactin is secreted autonomously in a characteristic pattern of two daily surges, one nocturnal and one diurnal. The present study investigated whether, during lactation, prolactin secretion occurred in an autonomous nightly surge pattern, in addition to secretion resulting from suckling stimulation. Nocturnal levels of prolactin were measured daily for 2 weeks in lactating rats which were separated from their young from 21.00 to 06.00 h. It was found that no nocturnal prolactin surges were present throughout the 2 weeks of lactation. In addition, it was observed that after pups were removed for 3 h prolactin levels were lower during the first week of lactation than during the second week. It was concluded that lactational dioestrus is distinguished from pseudopregnancy by the absence of autonomous secretion of prolactin in the pattern of a nocturnal surge.
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