Effects of bromocriptine on single nephron and whole-kidney function in rats.

Bromocriptine (BRC) is a semisynthetic ergot alkaloid possessing dopamine agonistic activity. We had previously observed significant changes in renal hemodynamics in rats pretreated with BRC to suppress endogenous prolactin plasma levels. To investigate further the effects of BRC on single nephron and whole-kidney function, micropuncture and clearance experiments were performed on euvolemic and volume-expanded rats pretreated with BRC (1 mg i.p.) or solvent. Both groups of BRC-pretreated rats had a significantly higher renal plasma flow and a lower arterial pressure, filtration fraction and renal vascular resistance than control (solvent-treated) rats. In volume-expanded rats, BRC caused a small but significant decrease in whole-kidney glomerular filtration rate (GFR) and an increase in superficial single nephron GFR; BRC did not affect GFR or single nephron GFR in euvolemic rats. Proximal tubular reabsorption and urinary excretion of water and electrolytes were not altered by BRC under conditions of euvolemia or volume expansion. It was concluded that BRC exerts a dopamine agonist-like effect to increase renal plasma flow and suppress endogenous plasma prolactin levels, whereas the urinary water and electrolyte excretion and superficial proximal tubular reabsorption are not altered appreciably. The increased ratio of single nephron GFR/GFR suggests that in volume-expanded rats, BRC redistributes glomerular filtration to superficial nephrons, possible by preferential dilation of superficial afferent arterioles.