Renal Sympathetic Nerves do not Modulate Renal Responses to Haemorrhage in Conscious Lambs

Abstract

The present study was designed to investigate the renal responses to hypotensive haemorrhage early in life and the role of renal sympathetic nerves in modulating these renal responses. To this end, experiments were carried out in conscious, chronically instrumented lambs with either intact renal nerves (n = 7, Intact) or bilateral renal denervation performed at the time of surgery (n = 5, Denervated). Parameters of renal function were measured before and after 20% haemorrhage (experiment 1) and 0% haemorrhage (experiment 2), the latter serving as a time control. The two experiments were performed in random order at intervals of 24‐48 h. Within 20 min of hypotensive haemorrhage in intact lambs, glomerular filtration rate decreased by ∼60%; this response was not altered by renal denervation. Since renal plasma flow remained constant after haemorrhage, the filtration fraction also decreased. After 20% haemorrhage, urinary flow rate decreased in intact lambs; this response was also not altered by renal denervation. Excretion rates of Na+ and K+ as well as urinary osmolality and free water clearance were not altered by haemorrhage in either intact or denervated lambs. These data provide the first description of renal responses to haemorrhage early in life. In addition, the present findings provide new information that renal responses to haemorrhage early in life do not appear to be modulated by renal sympathetic nerves.

Developmentally regulated effects of severe hemorrhage on cardiovascular homeostasis and the arterial baroreflex control of heart rate

“…In previous studies in conscious sheep, we reported some of the first comprehensive reports of the physiological responses to compensated hemorrhage in the newborn period (Smith and Abu-Amarah 1997 , 1998 ; Smith et al. 2000 , 2004 ; Smith 2002 ). These investigations revealed that the newborn appears to recruit different mechanisms to restore blood pressure following compensated blood loss as compared to later in life.…”

“…Although responses to severe blood loss early in life are not well characterized, our previous investigations in conscious, chronically instrumented developing sheep have provided some of the first comprehensive reports of the responses to nonhypotensive and moderate hypotensive hemorrhage (or so-called compensated hemorrhage) during postnatal maturation (Smith and Abu-Amarah 1997 , 1998 ; Smith et al. 2000 , 2004 ; Smith 2002 ). These findings show that hemodynamic, humoral, and renal responses to compensated hemorrhage are considerably different in the newborn period as compared to later in life: For example, after the onset of hemorrhage, there is a dramatic increase in heart rate in newborns but not young adult sheep, while blood pressure is maintained (Smith et al.…”