Effects of baroreceptor denervation on volume loading hypertension in anephric dogs.

Abstract

SUMMARY The role of the baroreceptor mechanism in determining the relationship between fluid volume and arterial pressure is not clear. Therefore, the effects of the baroreflex on the arterial pressure and fluid volume of conscious, anephric dogs were studied after a sustained 10% increase in blood volume. The animals were equipped with long-term indwelling arterial and venous catheters, and arterial pressure was monitored 24 hours a day. The increase in blood volume was achieved by intravenous infusion of 50 ml/kg of lactated Ringer's solution in 30 minutes. After volume loading arterial pressure increased rapidly to hypertensive levels (130.8 ± 7.5% of control) in a baroreceptor denervated group. The initial increase in arterial pressure in a group of normally innervated dogs was smaller (118.8 ± 1.8% of control), but by 24 hours postinfusion the arterial pressure of both groups had reached the same level. The innervated group had probably experienced baroreceptor resetting by this time. Blood volume both before and after infusion was not different in the denervated and innervated groups; however, sodium space was markedly higher before the infusion in the denervated dogs (431.8 ± 13.8 ml/kg vs 344.8 ± 19.0 ml/kg in the innervated dogs), and the volume load caused parallel increases in this space in the denervated and innervated groups. The present study shows that the blood volume of anephric dogs was unchanged after baroreceptor denervation while the extracellular fluid volume of denervated dogs was elevated. Furthermore, a small sustained increase in blood volume in either conscious, innervated dogs or conscious, baroreceptor denervated dogs, in contradistinction to the effects in anesthetized dogs, resulted in significant increases in arterial pressure (p < 0.05). (Hypertension 7: 562-568, 1985) KEY WORDS • blood volume • extracellular fluid volume • central venous pressure A LTHOUGH several investigators have studied / \ the effects of volume loading on the arterial A. ^L. pressure of either intact or baroreceptor denervated animals, 1 -2 little information is available about the effects of the arterial baroreceptors on the arterial pressure response to a step change in blood volume in conscious animals. The effects of the arterial barorefiex on fluid volume distribution also are poorly understood.When excess volume in the form of saline is infused continuously into dogs with reduced renal mass, blood volume progressively increases for a few days and then decreases to near control values after 1 week.

Cardiovascular responses to long-term blockade of nitric oxide synthesis.

“…16 The control value of SD of arterial pressure in their study was very close to the control SD in our study of 10.0 ±0.8 mm Hg, but our SD during L-NAME increased even more to 13.1±1.4 mm Hg. The variability of arterial pressure and heart rate reflects not only changes in baroreceptor reflex function as we have previously shown in sinoaortic-denervated dogs 32 but also activity and postural changes in dogs. 16 In the present study during L-NAME, the dogs were noticeably quieter, which may partially explain the decrease in heart rate variability.…”

Effect of Sinoaortic Deafferentation on Renal Wrap Hypertension

“…A similar observation has been made in SAD dogs in which anephric animals were challenged with a volume infusion. 23 In these animals, arterial pressure rose to a higher level than was observed in intact animals, but within 24 hours, the arterial pressure was similar in both groups of dogs. Although other studies have shown that SAD animals may develop a more rapid rise in MAP when renal hypertension in induced, 24,25 only 1 study has demonstrated an exaggerated and sustained MAP after renal hypertension in SAD animals.…”