The growth capacity of cultured vascular smooth muscle cells (VSMC) obtained from the thoracic aorta of 8-week-old male and female spontaneously hypertensive rats (SHR) was compared. Explants from the intima- media complex were cultured in Dulbecco minimum essential medium supplemented with fetal calf serum (10 %). The migration of VSMC out of the explants started on day 2 in both sexes but on day 18 the number of explants with VSMC migration was 100 ±32 explants/flask in male VSMC and only 24 ±5 explants/flask in female ones. The doubling time at the early exponential phase of growth was shorter (13.5 ±0.5 h) and the p H]-thymidine Labelling Index was higher (34.0±2.3 %) in male VSMC than in those from females (19.9±0.6 h and 23.9±1.9 %, p<0.01, respectively). The difference in the doubling time became even more apparent in the late exponential phase of growth (male VSMC: 51.8±2.0 h, female VSMC: 91.5±5.8 h, p<0.001). Moreover, at the end of the exponential growth phase, the male VSMC reached significantly higher (pcO.OOl) maximum population density than VSMC from females. Our data provide evidence of different growth characteristics of cultured VSMC isolated from male and female SHR aortas.
The role of age in the development of two-kidney, one-clip (2K1C) renal hypertension was evaluated. Blood pressure response to aortic constriction was more pronounced in young rats although the alterations of renal renin activity and body fluid volumes were greater in adult ones. Obtained results suggested that 2K1C renal hypertension is maintained by reciprocal interaction of renin-angiotensin system and body fluid volume alterations only in adult rats. In young rats other factors might be more important.
The growth response to angiotensin II (Ang II) was studied using cultured vascular smooth muscle cells (VSMC) isolated from the aortae of male and female spontaneously hypertensive rats (SHR). Systolic and mean arterial blood pressure of 10-week-old males was significantly higher when compared to age-matched females. The specific growth rate of male VSMC was significantly higher on the third and sixth day after synchronisation. Angiotensin II in concentration 10~7 M stimulated the specific growth rate only in male VSMC during the exponential phase of growth. Moreover, doubling time was 3 hours shorter in male VSMC in comparison with the females. Our results suggest that both the increased specific growth rate and augmented growth-response of male VSMC to Ang II may explain the higher sensitivity of males to hypertensive stimuli.
To evaluate the role of chloride in the pathogenesis of salt-dependent deoxycorticosterone (DOC) hypertension, we studied young Wistar rats chronically loaded with sodium bicarbonate (NaHCO3) or sodium chloride (NaCl) which were administered either in the diet or in the drinking fluid. Selective sodium loading (without chloride) increased blood pressure (BP) in DOC-treated animals only if NaHCO3 was provided in the diet. In contrast, no significant blood pressure changes were induced by DOC treatment in rats drinking NaHCO3 solution. Hypernatremia and high plasma osmolality occurred only in rats drinking NaCl or NaHCO3 solutions. Compared to great volume expansion in NaCl-loaded DOC-treated rats, the degree of extracellular fluid volume expansion (namely of its interstitial fraction) was substantially lower in both NaHCO3-loaded groups in which significant hypokalemia was observed. NaHCO3-drinking rats without significant blood pressure response to DOC treatment represented the only experimental group in which blood volume was not expanded. In conclusion, our data confirm previous observations that NaHCO3 loading is less potent in eliciting DOC hypertension than NaCl loading, but blood pressure rise in rats fed NaHCO3 diet clearly demonstrated that selective sodium loading could potentiate the development of DOC hypertension if NaHCO3 is offered within the appropriate dietary regimen. The reasons for the failure of NaHCO3-drinking rats to elevate blood pressure in response to chronic mineralocorticoid treatment are not obvious. However, the absence of a significant plasma volume expansion together with hypernatremia and increased plasma osmolality suggest a considerable degree of dehydration in these animals which fail to increase their fluid consumption compared to water drinking rats.