No abstract

Hyperthermic stress in rats results in increased fat c-AMP levels and causes alterations in liquid metabolism (Kampa and Frascella 1977). These changes are thought to be the result of elevations of lipolytic hormones as well as decreases of blood insulin levels. Although lowering the temperature had no effect on glucagon secretion in isolated perfused rat pancreas, hypergluconemia and reductions in blood insulin levels during hyperthermia have been demonstrated (Kampa and Frascella 1977;Kampa, Frascella, Hundertmark, Rosenberg and Reid 1981;Loubatieres-Mariani, Chapal, Puech, Lignon and Valette 1980). Data previously derived from isolated tissue experiments and isolated fat cells suggest that c-GMP increases follow c-AMP elevations and that c-GMP exerts an inhibitory effect on c-AMP (Asakawa, Ruiz and Ho 1978). In this experiment, epididymal fat c-GMP and c-AMP levels were measured in non-diabetic and streptozotocin diabetic rats with normal and hyperthermic rectal temperatures. Materials and MethodsForty adult male Sprague Dawley rats with a weight range of 220 to 280 grams were housed for twenty-one days in a temperature controlled room. Twenty animals were then injected with streptozotocin (50 mg/kg) i.v. via the saphenous vein to induce diabetes. A control group was injected with an equivalent volume of physiological saline. All animals were then maintained on ad libitum Purina Chow diet and water. One week following the injections, half of each group were placed into an environmental chamber where the humidity was maintained at 45 percent. The temperature was gradually increased to elevated the animals' rectal temperatures at a rate of approximately 1 °C every thirty minutes. Upon reaching a rectal temperature of 40 °C and then maintaining this temperature for about 30 minutes, the animals were removed and immediately killed by decapitation. Blood was collected from the trunk portion, and a portion of epididymal fat was removed and frozen in liquid nitrogen. The c-AMP and c-GMP was extracted from the epididymal fat pads by a method described by Steiner, Kipnis, Utiger and Parker (1969). c-AMP and c-GMP concentrations were obtained by radioimmunoassay (Steiner, Pagliari, Chase and Kipnis 1972). Blood glucose levels were determined by a hexokinase procedure (Slein and Bergmeyer 1963). Results and DiscussionHyperthermia resulted in epididymal fat c-AMP and c-GMP increases in non-diabetic and diabetic rats as compared to the cotrol group (Table 1). This data indicates that significant fat c-GMP elevations are associated with large increases in c-AMP, a finding that previously has been shown in vitro only. Further in vivo work is required in order to determine if there is a lag time between the rise of c-AMP and c-GMP and if c-GMP inhibits c-AMP elevations.