Effects of Isulin-like Growth Factor-I on Maternal and Fetal Plasma Amino Acid Levels in Pregnant Rats.

Abstract

ABSTRACT. Pregnant rats were subcutaneously administered with recombinant human insulin-like growth factor-I (rhIGF-I) in doses of 0 (control), 1, 2, and 4 µg/g body weight per day from day 18 to 21 of pregnancy. On day 21 of pregnancy, maternal and fetal plasma samples were collected and those amino acid levels were measured. The ratios of fetal/maternal plasma amino acids, especially l eucine, isoleucine, tryptophan, phenylalanine and tyrosine, increased in 2 µg rhIGF-I treated group. Both total fetal weight and total placental weight were also higher than those in the control group. These results suggested that IGF-I enhanced fetal growth by, as one of its possible mechanisms, promoting placental amino acid supplies from the mother to fetuses. KEY WORDS: insulin-like growth factor-I (IGF-I), plasma amino acid, pregnant rat.J. Vet. Med. Sci. 64(9): 859-861, 2002 Insulin-like growth factor-I (IGF-I) is widely known to be a major growth factor for many types of cells including placental cell [4] and also an important regulatory factor for fetal growth and development [11,16]. Fetal tissue and placenta expressed a large number of IGF receptor [12,14]. Gluckman et al. [6] demonstrated that the administration of recombinant human IGF-I (rhIGF-I) to pregnant rats enhanced fetal growth. In most species, maternal serum levels of IGF-I correlated positively with fetal and/or placental weight [7,15]. On the other hand, the supply of amino acids from the mother to fetuses via placenta is crucial importance for fetal growth. The full term fetal weight was reduced by the starvation at late phase of pregnancy with the decrease of fetal plasma amino acids level and also fetal/maternal plasma amino acids ratio in the rat [1]. Impaired fetal and placental uptake of amino acids has been observed in several models of growth retardation in the rat [8]. This note deals with the effects of IGF-I on maternal and fetal plasma amino acid concentrations in pregnant rats.Timed pregnant Wister ST rats (weighing 250-270 g) were obtained from Japan SLC (Shizuoka, Japan) and divided into four treatment groups. The rats were housed in standardized cages with controlled temperature under a 12-hr light-dark cycle and received standard rat chow and drinking water ad libitum. The rats were subcutaneously administered with rhIGF-I (Fujisawa Pharmaceutical Co., Ltd., Osaka, Japan) in doses of 0 (control), 1, 2, and 4 µg/g body weight per day in 0.6 ml of physiological saline, based on the previous reports [2,5,6] and our preliminary study. The total of 6 administrations was given every 12 hr to each rat starting from at 19:00 on day 18 of pregnancy. Three hours after the final administration on day 21, 1 day before delivery, the rats were anesthetized with diethyl ether. Then, blood samples collected from maternal artery were transferred into heparinized tubes on ice and centrifuged at 1,500 × g for 10 min at 4°C. Plasma samples were separated and stored at -20°C until assay. After blood sampling, individual placentas and fetuses were removed ...

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