Milk electrolyte content of Dahl hypertensive and normotensive rats

Effect of cross-fostering on blood pressure and renal function in the New Zealand genetically hypertensive rat

1. The severity of hypertension displayed by adult spontaneously hypertensive rats (SHR) and Dahl (SS/Jr) rats can be reduced by 20-30 mmHg if the hypertensive pup is cross-fostered to a normotensive mother within the first 2 weeks of birth. In the SHR, at least, this blood pressure-lowering effect arises through programming of the neonatal kidney to excrete sodium more effectively. Thus, cross-fostering may only be effective in lowering pressure in salt-sensitive hypertensive strains. Accordingly, the aim of the present study was to determine whether cross-fostering is effective in lowering adult blood pressure in the salt-resistant New Zealand genetically hypertensive (GH) rat. 2. Genetically hypertensive and control normotensive (N) rat pups were reared by either their natural mothers or a foster mother of the opposite strain (NX and GHX). Blood pressure was tracked from the age of 6-18 weeks, at which time renal function was assessed using standard clearance techniques in anaesthetized rats. Renal function was also assessed in a separate group of young rats at 5-6 weeks of age. 3. Cross-fostered GHX rats had lower blood pressure than GH rats, but this difference was only apparent until 9 weeks. The NX rats had higher blood pressures than N rats, but again pressure converged at 10 weeks. Basal renal function did not differ between GH and GHX rats or between N and NX rats at either age. However, young GH rats had lower renal blood flow, glomerular filtration rate, urine output and sodium excretion than N rats. 4. These data show that cross-fostering is effective in lowering blood pressure in GH rats, albeit transiently. The kidneys do not appear to play a role, because renal function did not differ under the current experimental conditions between GH and GHX rats. However, the kidney may play a greater role in the onset of hypertension in the GH rat than previously thought.

Modulation of blood pressure in the Dahl SS/jr rat by embryo transfer

Gestational hypertension and malnutrition are associated with hypertension and ischemic heart disease in the adult human. The impact of the gestational environment on the adult blood pressure in two well-characterized genetically homogeneous rat strains, the hypertensive SS/jr and normotensive SR/jr, was studied by cross-fostering within 6 hours of birth and by embryo transplantation with the recipient dam nursing the transplanted pups. Systolic blood pressure (BP) was measured by tail-cuff plethysmography twice a week after the age of 7 weeks. The lactational environment (cross-fostering) had no effect on blood pressure. Embryo transfer between like strains had no effect on the development of hypertension, nor did the BP of R transferred to S (RetS) differ from that of normal R or RetR. At 7 weeks of age, the BP of SetR was significantly lower than that of S or SetS (P<.01) and was similar to that of RetR and R. With age, the blood pressures of the S, SetS and SetR increased at approximately the same rate but from a significantly different baseline. Salt-sensitivity in the S and resistance in the R were not altered. The protective effect of the R gestational environment on SetR female BP was abrogated during whelping and lactation. Embryo transfer and cross-fostering did not alter the weight of rats older than 7 weeks. Because the BP of the R dams were significantly lower than that of the S dams, these studies do not distinguish between the effects of the R dams' lower blood pressure per se and hormonal influences of the R uterus on the S blood pressure phenotype.