Oxygen Consumption in the Spontaneously Hypertensive Rat

Abstract

The spontaneously hypertensive rat (SH) has been widely utilized as an animal model for the study of physiological functions as they pertain to essential hypertension in man. In a recent report, Wright et al. (1) demonstrated a marked decrease in the responsiveness to thermal stress in the SH rat which they, in part, attributed to deficient water mobilization for evaporative cooling. The possibility remained that changes in metabolic heat production, cardiovascular adjustments to heating or other factors which might accompany the development of hypertension could influence thermoregulation of hypertensive animals in hot environments.The work of Kloetzel et al.(2) demonstrating a high percentage of hypertensive individuals in industrial jobs requiring heat exposure has emphasized the need for studies to define stress responses in diseases such as hypertension in which the early symptoms may go undetected or the use of maintenance therapy combined with peer group pressure may encourage normal work and recreational activities. The limits which are described for physical exertion and exposure to environmental factors are nearly always based on data obtained from young, healthy individuals, and it may be reasonable to question their applicability to individuals exhibiting chronic alterations in physiological functions. In the present study, oxygen consumption and rectal temperatures of SH and normotensive rats were determined during exposure to a range of environmental temperatures designed to induce mild cold or heat stress. In an attempt to determine the nature of the observed differences, the effects of beta adrenergic blockage on 0 2 uptake in cool and warm environments was examined.Materials and methods. Male SH rats (blood pressure = 163 f 7 mm Hg and weight, 341 & 7 g) of the Okamoto-Aoki strain (3) and parent strain Wistar-Kyoto (WKY) normotensive (bp = 112 f 5 mm Hg and weight, 447 f 16 g) rats were examined at 15-20 weeks of age. Animals were housed at 24 f 1" and 50% relative humidity with a 14 hr light-10-hr dark photoperiod. Water and Purina rat chow were available ad libitum.Oxygen utilization was determined using the open flow system of Ben-Porat et al. (4). The animals were studied in 3.0 liter metabolic chambers submerged in a 170 liter waterbath held at 2 0.1" of the desired temperature. Room air was passed through the chamber at approximately 0.6 liter/min and the ambient temperature (Ta) in the chamber monitored with thermometers inserted into the chamber space. Water was absorbed on dryrite which had been incorporated into the inflow and outflow lines and in the chamber floor. Carbon dioxide absorbant (NaOH) was placed in the chamber floor and outflow lines. Air samples of about 1.0 liter were collected in Saran plastic bags at 30-min intervals over a 3.0-hr period for determination of 0 2 content with the Beckman E-2 0 2 analyzer. In order to avoid variations in the data associated with the early adjustment of the animal to the chamber environment, only the last three values were averaged and com...

Cardiovascular and metabolic responses of hypertensive and normotensive rats to one week of cold exposure

“…T a has sometimes been reported to have different effects on metabolic rate (V O 2 ) in SHRs and normotensive Wistar-Kyoto controls. Strain differences were reported in adult rats when T a was in the range 25-32°C (38) and in infant rats when the T a range was 17-23°C (18). However, others have reported no differences in V O 2 between these strains in cold (5°C) or warm (35°C) conditions (37).…”

Studies on thyroid activity in deoxycorticosterone-salt and Goldblatt two-kidney, one-clip hypertensive rats

“…In spontaneous hypertensive rats, agedependent variations (Rioux & Berkowitz 1977) and contradictory results in adult rats have been reported (Werner et al 1975;Kojima et al 1975;Wright et al 1978). In spontaneous hypertensive rats, agedependent variations (Rioux & Berkowitz 1977) and contradictory results in adult rats have been reported (Werner et al 1975;Kojima et al 1975;Wright et al 1978).…”

Vascular and renal function in experimental thyroid disorders

“…Several variables were studied to determine if thyroid weight increases were secondary to hyperor hypofunction of the gland, with T 3 and T 4 serum levels being the most frequently measured. In spontaneously hypertensive rats, age-dependent variations (170) have been seen and contradictory results in adult rats have been reported (167,170,171). A decrease in T 3 and T 4 serum levels in Dahl rats (172) and a reduction in T 3 serum concentrations in encapsulated hypertensive rats (169) were observed.…”