Abstract

The present experiments studied the ontogeny of sympathetic control of the renin-angiotensin system by using pharmacological agents, which act at different levels of the sympathetic axis, to increase plasma renin activity (PRA) during the preweanling period in Sprague-Dawley rats. The selective beta-1 adrenoceptor agonist, prenalterol, produced age- and dose-dependent PRA increases. In 5- and 10-day-old animals, prenalterol treatment produced minimal stimulation of PRA and the dose-response curve was essentially flat. In contrast, greater PRA responses to increasing doses of prenalterol were found in 15- and 20-day-old animals. The PRA response to tyramine, which causes norepinephrine release from postganglionic sympathetic fibers, gradually increased between 5 and 20 postnatal days of age, first producing significant stimulation on day 15. Centrally mediated sympathetic activation with yohimbine also produced age-dependent stimulation of PRA that was comparable to the increases produced by tyramine between postnatal days 10 and 20. However, in contrast to tyramine, yohimbine produced a significant increase in PRA on postnatal day 5. The present results suggest that functional sympathetic control of the renin-angiotensin system matures during the second to third postnatal week in the Sprague-Dawley rat, and this may be related to the development of beta-1 adrenoceptors in the kidney that regulate renin release.