Failure to maintain steroid hypertension during pregnancy in the rat

Abstract

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 *

Progesterone Is Not Responsible for the Blood Pressure Fall in Late-Pregnant New Zealand Genetically Hypertensive Rats

“…In genetically hypertensive rats of the Oka-mot0 (SH) strain, and in rats with other forms of experimental hypertension, blood pressure falls progressively during the last week of pregnancy to nearly normotensive levels, remains reduced through parturition, and then returns rapidly to prepregnancy hypertensive levels by the first or second day postparturition (1)(2)(3)(4)(5). Also during the last week of pregnancy in the rat, plasma progesterone levels rise, reaching a sustained peak at a time coinciding with the reduction of blood pressure, and then fall rapidly, returning to prepregnancy levels at a time coinciding with the return of blood pressure to hypertensive levels (4,6).…”

“…For example, in rats made hypertensive by mineralocorticoid treatment and excess sodium chloride intake, blood pressure was reported to fall during late pregnancy by some investigators (3,5), while others reported no such effect ( 1 1, 12). Second, in pregnant rats plasma progesterone rises to a maximum on Days 15-20, then falls back to prepregnancy values by Day 1 postparturition (6); blood pressure in pregnant hypertensive rats changes in a mirror-image fashion with respect to progesterone, falling from about Day 15 of pregnancy to a minimum level on Days 20-21, then rising rapidly back to prepregnancy values by the first or second day postparturition (4,5). Despite extensive investigation, the mechanism underlying this rapid reduction of blood pressure, and the subsequent and even more rapid rise back to hypertensive levels, has not been defined.…”

"Papel do endotélio na reatividade vascular de ratas com hipertensão espontânea ao término da gestação"

“…Acidentalmente observado em cães hipertensos, ainda na primeira metade o século passado (GOLDBLATT; KAHN;HANZAL, 1939), evidenciou-se que ocorria um decréscimo intenso da pressão arterial ao término da prenhez, a ponto de atingir nível de normotensão (PAGE et al 1940). Dentre as hipóteses sugeridas para tal fenômeno, causas endocrinológicas e placentárias já foram estudadas MOORE;BILICZKI,1968;SYBULSKI;TOTH;MAUGHAN, 1971). Em seguida, evidenciouse que várias espécies animais como ratos, coelhos e ovelhas também se comportavam da mesma maneira e desenvolviam tais adaptações hemodinâmicas durante a gestação (MOLNAR; HERTELENDY,1992; COELHO; BALLEJO; SALGADO,1997;THORNBURG et al, 2000) de forma semelhante ao que também acontece na espécie humana.…”