SummaryWeight gain and food intake were measured in unstressed nonpregnant and pregnant guinea pigs fedad libitum.Nonpregnant females consumed 33.2 ± 0.5 g·day“−1of 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−1at 27 days to over 60 g·day−1near 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 ± 0.36versus5.65 ± 0.25;P< 0.05), whereas the pregnant animals responded with a substantial increase in blood glucose (7.57 ± 0.48versus5.87 ± 0.33;P< 0.05). Lactate was increased intraoperatively in both groups (1.76 ± 0.22versus1.11 ± 0.07, nonpregnant; 1.80 ± 0.17versus1.10 ± 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, β;-hydroxybutyrate, acetoacetate, and free fatty acids did not change consistently with gestation and were not significantly different from nonpregnant values.SpeculationIn animal studies, it is frequently difficult to differentiate the effects of advancing gestation from the effects of acute sample collection. Extension of these techniques of chronic catheterization to other areas of guinea pig metabolism and to other small mammalian species may provide more uniform conditions for the study of the comparative physiology of gestation and fetal development.