Effects of Prolactin Administration and Suppression on Blood Pressure and Body Fluid Compartments in the Rat*

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Abstract
The effects of chronic hyper- and hypoprolactinemia on blood pressure (BP), body fluid compartments, and renal function in male rats were studied. Chronic hyperprolactinemia was induced by administration of ovine PRL (oPRL) over 7 days at a rate of 8.9 μg/h via an ip osmotic minipump. Hypoprolactinemia was induced by lergotrile mesylate (LM), administered at 10.0 μg/h via osmotic pump. In addition, several rates of oPRL administration (0.6, 2.9, 5.7, 11.3, and 22.7 μg/h) were studied. Total body water, extracellular fluid volume (ECF), and plasma volume were determined by dilution of 3H2O, 35SO4, and 51Cr-chloride, respectively. BP increased after oPRL administration at 0.6 μg/h (P < 0.001) and decreased after oPRL administration at 8.9 μg/h (P < 0.001) and 22.7 μg/h (P < 0.01). The oPRL (8.9 μg/h) -induced fall in BP was associated with an increased ECF (P < 0.05) and plasma volume (P < 0.05). Total body water was unchanged in all studies. Similar to the high dose oPRL administration, LM also lowered BP and increased ECF. Plasma sodium, potassium, and osmolality were unchanged after oPRL (8.9 μg/h) or LM treatment. No change in renal creatinine, osmolar, free water, sodium, and potassium clearances from control values were observed with any treatment, except that oPRL decreased potassium clearance on day 7 (P < 0.05). Since vasopressin is known to contaminate many oPRL preparations, identical studies were carried out after administration of the vasopressin analog desmopressin acetate. This analog failed to mimic any of the effects observed after oPRL administration; thus, it is unlikely that the observed changes are attributable to vasopressin contamination of oPRL. These data suggest that oPRL increases BP at low doses and decreases BP at high doses in the male rat. oPRL at high doses is associated with fluid shifts from the intracellular to the extracellular compartment. High rates of oPRL administration mimicked the effects of LM on BP and body fluid compartments, whereas low rates of oPRL administration had effects on BP opposite to LM.

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