A micropuncture study of the renal response to haemorrhage in rats: assessment of the role of vasopressin

Abstract

SUMMARYThe acute effects of haemorrhage (15 ml (kg body wt)-') on renal function at whole-kidney and single-nephron levels were studied in Inactin-anaesthetized rats. In order to assess the role of vasopressin in mediating the haemodynamic effects, responses in untreated Long-Evans rats were compared with those in Brattleboro rats (which lack circulating vasopressin) and in Long-Evans rats treated with a V1 receptor antagonist. In time-control animals, there were no significant changes in mean arterial pressure (MAP), excretion rates, glomerular filtration rate (GFR), superficial-nephron GFR (SNGFR) or fluid reabsorption in the superficial proximal tubules during the course of the experiment. Following haemorrhage, the immediate reduction in MAP was followed in each group by partial recovery for 30 min; thereafter, MAP was stable. In untreated Long-Evans rats, haemorrhage was followed by a 26 % reduction in GFR (P < 0-001, measured 60-150 min post-haemorrhage) and a larger reduction (45 %, P < 0.001) in SNGFR, so that the SNGFR/GFR ratio fell significantly ((27.9 + 1.9) x 10-6, control period; (20.2 + 2-2) x 10-6, post-haemorrhage, P <0.01). Slightly greater reductions in GFR and SNGFR were seen in Brattleboro rats and V, antagonist-treated Long-Evans rats, which corresponded to slightly greater haemorrhage-induced reductions in blood pressure in these groups; the falls in the SNGFR/GFR ratio were similar to that in untreated Long-Evans rats. In all three groups of bled rats, fractional reabsorption by the proximal convoluted tubule increased slightly 30-60 min after haemorrhage, but during the subsequent period (60-150 min) returned to values indistinguishable from those during the control period. The results suggest that the renal haemodynamic changes that follow moderate haemorrhage include a preferential reduction in the GFR of superficial nephrons. Vasopressin appears to play no role in this response. Increases in fractional reabsorption in the proximal tubules are seen only during the immediate post-haemorrhage period.

Glomerular haemodynamics during renal artery clamping and haemorrhage in the dog

“…We obtained very similar findings in our dogs: the SNGFR/GFR ratio fell during HH but remained unchanged during C (Tables 3 and 4). We agree with the interpretation by Shirley & Walter (1995) …”

“…Thus, although the Kf value showed 'a surprising tendency to rise' (Shirley & Walter, 1995) in our earlier paper, this nonsignificant tendency is not present now. On the contrary, Kf decreased in period 4 (MAP, 60 mmHg) in dogs with HH; since anuria was present in this period and since the kidney visibly $hrank, this finding must be treated with caution.…”

“…No attempt was made to analyse this finding further; from our earlier experiments, however, angiotensin II (Heller & Horatcek, 1990), leukotrienes (Heller, Horacek & Kamaradova, 1988 a) and thromboxanes (Heller, Horacek & Kamaradova, 1988 b) are possible candidates for causing this type of constriction in anaesthetized dogs. Shirley & Walter (1995) found a 26 % reduction in GFR in their rats whose MAP had been decreased to 85 mmHg by haemorrhage, while Pollock & Banks (1991) could find no change in GFR after a similar drop of RPP due to aortic clamping in rats. This situation is similar to that in our dogs.…”

Intraluminal ATP Concentrations in Rat Renal Tubules

“…There is evidence that ischemia induces ATP release in nonrenal tissues (25,28), and it has been proposed that intraluminal ATP might serve to protect the renal tubular epithelium under ischemic conditions by inhibiting energyconsuming transport processes (16). Moreover, we have shown previously that the partial renal ischemia that follows hemorrhage has little effect on fractional proximal tubular reabsorption (29) despite enhanced activity of the renal sympathetic nerves and the renin-angiotensin system; it seems that the stimulatory effects of these systems are offset by an inhibitory effect of unknown source. In the event, although hypotensive hemorrhage seemed to cause a marked increase in intratubular ATP concentration in two animals (contrasting with the stability seen in time controls), in the group as a whole, there was no statistically significant change.…”

Characterization of noradrenergic transmission at the dorsal motor nucleus of the vagus involved in reflex control of fundus tone

“…We employed isoflurane in our current study, whereas they employed a relatively high dose of Inactin (150 -200 mg/kg ip). The usual dose of this anesthetic is 80 -125 mg/kg ip (2,5,14,15,25,26,28,30).…”