Age-dependent renal effects of intrarenal dopamine infusion

Three groups of anesthetized puppies 16.4 +/- 1.2 (group I), 29.6 +/- 1.6 (group II), and 49.8 +/- 2.5 (group III) days of age were used to assess the renal response to graded doses of dopamine infusion into the renal artery. Dopamine infusion at 1 microgram X kg-1 X min-1 increased renal blood flow (RBF) from 3.61 +/- 0.31 to 4.22 +/- 0.43 ml X min-1 X g kidney wet wt-1 (P less than 0.05) only in the older puppies (group III). Glomerular filtration rate (GFR) increased in groups II and III from control values of 0.69 +/- 0.14 and 0.61 +/- 0.08 to 1.08 +/- 0.19 and 0.83 +/- 0.05 ml X min-1 X g kidney wet wt-1, respectively (P less than 0.05). However, urinary flow rate and sodium excretion were variably affected. Because dopamine is known to stimulate both alpha- and beta-adrenoceptors in addition to dopamine receptors, two additional groups of puppies 11.2 +/- 1.2 (group IV) and 72.8 +/- 2.4 (group V) days of age were studied to evaluate the renal effects of dopamine during the continuous intrarenal infusion of phentolamine and nadolol (an alpha- and a beta-adrenergic blocker, respectively). Dopamine elicited increases in RBF only in the older puppies (P less than 0.05). GFR, urinary flow rate, and sodium excretion increased in both groups; however, the magnitude of the change was greater for each parameter in the older group (P less than 0.05). These experiments suggest a maturational process for specific dopamine receptors and/or effector response, which may affect the observed age-dependent increases in RBF, GFR, and renal sodium handling.