beta-Adrenoceptor modulation of renin response to short-term reductions in pressure in young SHR

The increase in renin secretion in response to short-term (5 min) reductions in arterial pressure has recently been shown to be similar in young spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) animals. This was puzzling, since tonic renal nerve activity is thought to be elevated in the young SHR, and this has the potential to enhance the renin response. The purpose of the present investigation was to determine whether beta-adrenoceptor modulation of pressure-dependent renin release is diminished in the SHR. In conscious, age-matched SHR, WKY, and Sprague-Dawley rats, the effect on arterial plasma renin activity of 5-min reductions in renal perfusion pressure to 90 and 50 mmHg was determined before and during beta-adrenoceptor activation with isoproterenol or beta-adrenoceptor blockade with propranolol. Isoproterenol augmented the renin response at 50 mmHg in all three strains, with the greatest effect occurring in the Sprague-Dawley rats. The response at 90 mmHg was also enhanced in the SHR and Sprague-Dawley rats, but not the WKY rats. Propranolol had no effect in the SHR and WKY animals, but significantly reduced the renin response at 50 mmHg in the Sprague-Dawley rats. Thus, under the conditions of the present investigation (i.e., short-term reductions in pressure), tonic renal nerve activity does not affect pressure-dependent renin release through a beta-adrenergic receptor mechanism in either the SHR or WKY rats. However, under conditions of acute beta-adrenoceptor activation, the renin response is enhanced at a higher renal perfusion pressure in the SHR than in the WKY rat.