Gender Differences in the Dietary Lard-Induced Increase in Blood Pressure in Rats

Abstract

Abstract-We investigated the difference between male and female rats in the increase in blood pressure (BP) when they were fed a lard-enriched diet. We also investigated the effect of a gonadectomy, with or without testosterone treatment, on the dietary lard-induced increase in BP. Wistar-strain male or female rats were bilaterally castrated or ovariectomized. Some of them were implanted subcutaneously with silicon tubes containing crystalline testosterone. Each group was fed either chow alone or chow in which 50% of the energy content was from substituted lard. Systolic blood pressure (SBP) was determined weekly during each 7-or 11-week feeding period. A steady-state plasma glucose method was used to determine the insulin sensitivity. The dietary lard-induced increase in SBP was observed at 5 weeks after the start of the feeding in the sham-operated male rats. In the sham-operated female rats, SBP did not change from the basal values until 11 weeks into the experimental period. Castration eliminated the dietary lard-induced increase in SBP. Ovariectomy had no effect on SBP throughout the experimental period in both diet groups. In castrated males given testosterone, SBP increased in a dose-dependent manner. In ovariectomized females given testosterone, SBP increased significantly in the lard-enriched diet group. The dietary lard developed an insulin resistance in both the sham-operated and gonadectomized rats. However, SBP increased only in the sham-operated male rats. These results suggest that the dietary lard-induced increase in SBP depends on the presence of testosterone. Key Words: blood pressure Ⅲ rats Ⅲ insulin resistance Ⅲ diet Ⅲ hormones Ⅲ gender A sexually dimorphic pattern has been observed in relation to blood pressure. The prevalence of essential hypertension is higher in men than in age-matched premenopausal women. 1,2 In hypertensive rat models, such as spontaneously hypertensive rats (SHR) 3,4 and Dahl-salt hypertensive rats, 5,6 males have higher blood pressures than do females.Although the mechanisms of the gender difference in regulating blood pressure have not been completely elucidated, some studies have demonstrated that androgen has a potential role. 3,4,7 It was reported that an increase in blood pressure was attenuated by castration in the hypertensive rat model. 3,4,7 Furthermore, the relationship between androgen and pressure-natriuresis is suggested to play a part in the mechanism of these genetic forms of hypertension. However, whether or not male hormones may increase blood pressure remains uncertain in the other forms of hypertension.We recently verified that some fat-enriched diets led to the development of an increase in systolic blood pressure (SBP) in male rats compared with pair-fed control animals. 8 In the study, the chronic feeding of 8-week-old male rats with a lard-enriched diet increased SBP 5 weeks after the start of the feeding. And the chronic lard feeding induced hyperinsulinemia and led to the development of insulin resistance. An insulin sensitivity enhancer, trog...

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