Neurogenic control of peripheral resistance in renal hypertension

Importance of the sympathetic nervous system in the development of renal hypertension in the rat

1. Chemical sympathectomy with 6-hydroxydopamine (6-OHDA) prevented the development of renal hypertension in 80% of weanling male rats of the C.F. strain.2. Adult male rats treated with 6-OHDA developed hypertension on bilateral clamping of the renal arteries.3. Demedullation of the adrenal glands followed by 6-OHDA treatment in adult rats prevented the development of hypertension in 75% of them.4. Weanling rats treated with 6-OHDA did not have any measurable catecholamines in their hearts up to 72-78 days after treatment.5. Unlike the weanling rats, the hearts of adult rats (demedullated or with intact medulla) showed significant refilling (40-50%) of catecholamine stores 60 days after 6-OHDA treatment.6. It is concluded that the functional sympathetic nervous system is important in the development of renal hypertension in the rat.

Cardiovascular reactivity in the experimental hypertensive rat

1. In pithed preparations, deoxycorticosterone (DOCA)/NaCl-induced hypertensive rats showed increased cardiovascular reactivity to injected noradrenaline, DMPP, tyramine, angiotensin and to sympathetic nerve stimulation.2. Pithed, chronic renal hypertensive rats showed similar hyperreactivity to noradrenaline, DMPP and tyramine but responses to sympathetic nerve stimulation were within normal limits.3. In the isolated, Krebs perfused mesentery preparation, vessels obtained from both DOCA/NaCl and renal hypertensive rats showed hyperreactivity to injected noradrenaline. Responses to periarterial nerve stimulation were also markedly increased in preparations from DOCA/NaCl hypertensive rats, while preparations from renal hypertensive rats showed this effect only at higher rates of stimulation (12 and 25 Hz).

The contribution of the sympathetic nervous system to the development and maintenance of experimental hypertension in the rat

1. Experimental hypertension in the rat, induced either by renal artery stenosis or by treatment with deoxycorticosterone acetate (DCA) developed maximally over a period of 8 weeks. In both types of hypertension the rate of development was unaffected by immunosympathectomy or by chemical sympathectomy following the administration of 6-hydroxydopamine.2. The effect of 6-hydroxydopamine on chronic renal hypertensive rats was to produce a hypotensive action of longer duration than when similarly administered to DCA-induced hypertensive or normotensive rats. Reserpine (5-10 mg/kg intraperitoneally) produced a more marked hypotensive effect on both types of hypertensive rats although it was of much shorter duration.3. It is concluded that experimental hypertension of renal origin or induced by DCA treatment can develop even though most of the sympathetic nervous system has been destroyed. The maintenance of chronic hypertension in these conditions may depend on the adrenal glands or a hormonal system as yet undetected.