Some Aspects of Maternal Metabolism Throughout Pregnancy in the Conscious Rabbit

854 GILBERT ET AL. 003 1-3998/84/1809-0854$02.00/0 PEDIATRIC RESEARCH Copyright O 1984 International Pediatric Research Foundation, Inc. Vol. 18, No. 9, 1984 Printed in U.S.A. Some Aspects of Maternal Metabolism Throughout Pregnancy in the Conscious Rabbit MARC GILBERT, WILLIAM W. HAY, JR., ROBERT L. JOHNSON, AND FREDERICK C. BATTAGLIA Division of Perinatal Medicine, Departments of Pediatrics and Obstetrics-Gynecology, University of Colorado School of Medicine, Denver, Colorado 80262 Summary Studies of maternal metabolism during pregnancy have focused principally upon the latter half of gestation. However, maternal metabolic adaptations to pregnancy may occur at all stages of pregnancy. To study maternal metabolism throughout pregnancy, we developed a chronically catheterized rabbit model in which animals could be studied under conscious, stress-free conditions when nonpregnant and then serially throughout pregnancy. Anesthesia produced marked hyperglycemia. In contrast, chronic catheterization and daily handling did not affect blood concentrations of glucose, lactate, ketone bodies, or free fatty acids, or food intake. Glucose concentrationdecreased with pregnancy to a value at term equal to 85%of the prepregnancy value. Lactate concentration rose significantly in the second half of pregnancy but changes in free fatty acids and ketoacid levels were not significant. These results are discussed from a comparative physiologic point of view, emphasizing the unique aspects of rabbit metabolism during pregnancy and the importance of performing such studies under conscious, stress-free conditions. animal, free of surgical and anesthetic stress. Serial measurements of blood metabolite levels (glucose, lactate, free fatty acids, ketone bodies) and hormone levels (insulin and glucagon) were measured on the same animal before pregnancy and throughout pregnancy. These data provide an additional dimension for interspecies comparisons of the effects of pregnancy upon maternal metabolism including data for the very earliest pregnancy stages. MATERIALS AND METHODS Nonpregnant New Zealand White rabbits were obtained from a commercial breeder. Animals were housed in stainless steel cages and fed ad libitum a solid rabbit diet (Purina Rabbit Chow). The food intake was determined gravimetrically each morning. Surgery was camed out on nonpregnant rabbits. Animals were anesthetized with ketamine hydrochloride (35 mg. kg-' IM) and xylazine hydrochloride (6 mg. kg-' IM). Using sterile technique, a 20-gauge polyvinyl catheter was introduced into the right carotid artery and advanced into the left ventricle. Another polyvinyl catheter of the same size was introduced into the contralateral jugular vein. Catheters were tied in place and seThe impact of pregnancy upon maternal metabolism of car- cured with tissue adhesive (No. 9 10 Eastman Kodak). The cathbohydrates and lipids has been studied in the rat (14,20), guinea eters were tunneled under the skin to exit into a capped plastic pigs (I I, 37), and man (8, 18, 30). In these species, most studies cap sutured to the back of the neck (37). Catheters were filled were performed over the latter third of gestation. It is probable with a heparin solution (200 units/ml of 0.9% NaCl) and were that the timing and the magnitude ofmaternal metabolic changes flushed with this solution every 3 days. The catheters were kept during pregnancy may be related to such factors as the growth patent for withdrawal for at least 5 weeks. The arterial catheter rate of the fetus and the placenta, the fetal and placental mass was used to draw blood samples and the venous catheter was and metabolic rate at different stages of pregnancy, and the used for any infusions. maternal diet. In particular, animal species with a relatively short The rabbits were allowed to recover from surgery for at least gestation that produce a large fetal to maternal mass ratio at 2 days. A week later they were bred by artificial insemination term (i.e., guinea pig, 0.50; rat, 0.17; and rabbit, 0.15) are of (4). Females were injected intravenously with 5 mg of pituitary interest with regard to the maternal metabolic changes which luteinizing hormone (Armour-Baldwin Laboratories, Omaha, occur during the entirety of gestation. NE) (25), and immediately thereafter 0.5 ml of freshly collected The majority of metabolic studies during pregnancy have semen from a buck was injected into the vagina. involved surgical, anesthetic, and handling stress. In particular, The rabbits were handled daily, in a gentle manner, by the in the rabbit there have been no studies describing maternal same two persons. The rabbits were kept in standard stainless metabolism at any time of pregnancy under chronic, stress-free, steel cages which were darkened by drapes except at the front. steady state conditions. The present paper describes our results Studies and sampling were performed with the rabbit in this in developing techniques for chronic catheterization of rabbits same cage, or, after adaptation, in an 8 x 8 x 16 inch plastic prior to pregnancy, permitting metabolic studies in the conscious tray open at the top. No attempt was made to restrain the rabbits. These careful methods of handling were necessary to ensure Received November 30, 1982; accepted March 12, 1984. stability of the rabbit for chronic, stress-free studies. In this Address reprint requests to William W. Hay, Jr., M.D., University of Colorado regard, the rabbit poses a unique challenge for careful chronic School of Medicine, Box B 195, Department of Pediatrics, 4200 East Ninth Avenue, handling quite unlike the guinea pig which tolerates movement Denver, CO 80262. This work was supported by National Institutes of Health Program Grant and handling without significant difficulty (37). HW078I. W. W. H., Jr. is the recipient of a Special Emphasis Research Career Arterial blood samples were obtained every 2 to 3 days between Award (Diabetes Mellitus: Pediatric Aspects), National Institutes of Health, Na0900 and 1000 h for substrate and hormone determinations. tional Institute of Arthritis, Diabetes, and Digestive and Kidney Diseases-National Whole blood glucose concentration was measured with a glucose Institute of Child Health and Human Development. R. L. J. was supported by National Institutes of Health Training Grant HD07 186. oxidase method (I 6). Concentrations of lactate, acetoacetate, and 855 PREGNANT RABBIT METABOLISM P-hydroxybutyrate in whole blood were determined by standard enzymatic methods after perchloric acid precipitation (12). Serum free fatty acids were determined by the method of Ho (15). Immunoreactive insulin was measured with a heterologous immunoassay system as previously described (19). The standard hormone was crystalline rabbit insulin (22.7 U/mg; batch K 13369) supplied by Novo Industry, Copenhagen, Denmark. Immunoreactive glucagon was assayed using specific antibody (30K) for pancreatic glucagon (1). For each hor (...truncated)