Substrate concentration changes during pregnancy in the guinea pig studied under unstressed steady state conditions

Weight gain and food intake were measured in unstressed nonpregnant and pregnant guinea pigs fed ad libitum. Nonpregnant females consumed 33.2 +/- 0.5 g.day-1 of pellet diet and did not demonstrate a consistent pattern of weight gain. The average daily food intake of pregnant animals increased linearly from 38 g.day-1 at 27 days to over 60 g.day-1 near term, and the average maternal weight gain was 13.3 g.day-1. Using sterile technique, polyvinyl catheters were inserted under anesthesia into the carotid and femoral arteries of these animals. Animals recovered spontaneously, and catheters remained patent for up to 4 wk. The effect of surgical and anesthetic stress was evaluated by measurement of food intake and metabolite levels after surgery. In the nonpregnant animals, blood glucose decreased immediately after surgery (4.76 +/0- 0.36 versus 5.65 +/- 0.25; P less than 0.05), whereas the pregnant animals responded with a substantial increase in blood glucose (7.57 +/- 0.48 versus 5.87 +/- 0.33; P less than 0.05). Lactate was increased intraoperatively in both groups (1.76 +/- 0.22 versus 1.11 +/- 0.07, nonpregnant; 1.80 +/- 0.17 versus 1.10 +/- 0.08, pregnant). The pregnant animals differed from the nonpregnant animals with regard to the pattern of changes in blood ketones after surgery. The nonpregnant animals achieved steady state within 1 day after surgery, whereas the pregnant animals required 4 days for recovery. Food intake and maternal weight gain were markedly reduced during the recovery period for the pregnant animals. Blood metabolite levels were measured in well-fed, unstressed pregnant and nonpregnant guinea pigs. Using measurements made after the third postoperative day, the unstressed pregnant animals demonstrated a progressive decline in blood glucose levels, reaching levels significantly below those of nonpregnant animals at 55 to 60 and 60+ days. Arterial concentrations of lactate, pyruvate, beta-hydroxybutyrate, acetoacetate, and free fatty acids did not change consistently with gestation and were not significantly different from nonpregnant values.