The effects of protein-free diet were studied in the rat. It was shown that the diet led to a decrease in total serum protein, in plasma renin activity, in plasma renin substrate and in blood pressure; and to an increase in haematocrit. A significant linear correlation was found in every combination between the total serum protein, plasma renin activity, plasma renin substrate and systolic blood pressure. In contrast to the plasma renin activity, the renin concentration in the kidney of rats on a protein-free diet was found not to be lower that of the control group. The protein-free diet caused a decrease in the pressor response to injected angiotensin II.
PAGE AND GLENDENING (1953) and Moore (1965) concluded that experimental steroid hypertension, produced by administration of DOCA and saline to the unilaterally nephrectomised rat, was maintained during pregnancy. Both reports emphasise that this fhding is in contrast to the behaviour of clip or Goldblatt hypertension, which according to all workers shows a progressive fall of blood pressure from about the middle of pregnancy until delivery, This difference is said to support the view that hypertension in pregnancy is possibly related, directly or indirectly, to adrenal steroid activity.We have therefore measured the blood pressure daily during the late antepartum and early postpartum periods in rats with steroid hypertension; we found that it fell during pregnancy, and reached the lowest level just before delivery, but returned to higher levels in the puerperium.Animals. Virgin Wistar Albino rats imported from a dealer and weighing between 136 and 240 g. at the beginning of the experiments were used throughout. They were fed on normal rat meal (MRC formula). Although the weights of the animals covered a wide range there were sufficient numbers in each group for valid comparisons to be made; in any event there was no difference in response between animals of widely different weights.Hypertension. After a preliminary period of about 2 wk, during which the basal blood pressure was determined, the animals were divided into 9 groups, each of which was subjected to a different experimental procedure designed to produce steroid hypertension (table). Deoxycorticosterone acetate (Organon, Ltd) was given as a 100 mg. nuchal implant, and cortisone (Adreson: Organon, Ltd) was given daily intramuscularly in a dose of 1 mg. per 100 g. body weight. Left nephrectomy was carried out by a dorsal approach and NaCl was given as a 1 per cent. solution by mouth.The blood pressure was measured with the tail plethysmograph (van Proosdij- Hartzema, 1953-54). In this study the normal blood pressure varied between 60 and 90 with a mean of 75.3 mm. Hg. In the experimental animals the blood pressure was measured every 2nd day in the period before mating, and for the first 14 days of gestation. After this time readings were usually obtained daily until delivery, and frequently in the early puerpecium.In all groups the blood pressure began to rise after about a week of the experimental procedure, but the levels attained differed from group to group. In group 1, for example, hypertensive levels of over 110 mm. Hg were achieved, but in groups 8 and 9 the height differed only slightly from the normal.Gestarion. At about 3 wk the animals were mated overnight, and the day on METHOD AND MATERIAL9 *
Experimental deciduomata and progesterone together lower the blood pressure in the steroid hypertensive rat from the 5th to 10th day of decidual growth i. e. from the 10th to 15th day of pseudopregnancy. This would suggest that the fall of blood pressure at an equivalent time of gestation in hypertensive pregnant rats could be due to the maternal decidua under the influence of progesterone. It is further considered that the metrial gland of the deciduoma is more likely to be responsible for the hypotensive effect and by comparison that the metrial gland is implicated in the hypotensive effect of pregnancy. Progesterone alone also exerts a minor hypotensive effect in those animals in which a nephrectomy forms part of the hypertension regimen and indicates one way in which a maternal renal factor could influence blood pressure responses in hypertensive pregnant rats.
Experimental deciduomas which are maintained for 5 to 6 days do not lower the blood pressure in steroid hypertensive rats. In animals maintained longer only the metrial gland of the deciduoma survives but this too does not have a hypotensive action. It is concluded that the maternal decidual reaction in pregnant hypertensive rats is not responsible for the fall of blood pressure when this occurs at an equivalent time of gestation of up to 10 or 11 days and that the metrial gland is not responsible for the fall of blood pressure at whatever time the fall occurs during gestation.
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