Insulin-Like Growth Factor-I as a Follicular Growth Promoter during Early Pregnancy in Thoroughbred Mares

Abstract

ABSTRACT. To elucidate the physiological role of insulin-like growth factor-I (IGF-I) during early pregnancy in mares, number of ovarian follicles was monitored ultrasonically during different stages of the first trimester of pregnancy in 36 thoroughbred mares. From 9 of 36 mares, blood samples were collected weekly from the mating day till the end of the first trimester of pregnancy and plasma IGF-I profiles were examined with other hormones, like follicle stimulating hormone (FSH), luteinizing hormone (LH), ir-inhibin, progesterone and estradiol-17β. Plasma IGF-I level fluctuated throughout the studied period with four peaks on the 7th, 28th, 49th and 84th days of pregnancy. Plasma IGF-I showed a positive correlation with plasma FSH (P<0.05), whereas no correlation was found with other hormones during the studied period. Plasma IGF-I had no correlation with the foetal size, but positive correlation with the number of large (> 30 mm) and medium (10-30 mm) follicles. These results suggested that IGF-I might produce from the medium and large follicles during early pregnancy and promote to develop their growth via pituitary FSH mediated effects in the mares. The development and growth of the equine fetus represents the result of a complex interaction among specific regulating factors. The different growth factors were recently investigated to define their role in the regulation of proliferation and differentiation mechanisms during fetal life [3]. Studies regarding the development of the growth factors and their regulation during the fetal-neonatal period are still insufficient and often in disagreement [1]. During human early pregnancy, IGF-I and IGF-II display different spatial and temporal patterns of expression suggesting a role for them in the process attachment and implantation [16]. Little is known about the role of insulin-like growth factor-I (IGF-I) during early pregnancy in mares.The objective of this study was to characterize the profiles of plasma IGF-I during the first three trimester of pregnancy in thoroughbred mares, and to determine their relations with the embryonic (before Day 40 of pregnancy) or fetal (after Day 40 of pregnancy) growth and the follicular growth during the first trimester of pregnancy. Moreover, relations of plasma IGF-I profiles with other hormones were characterized. MATERIALS AND METHODS Animals:The experiment was conducted during the breeding season of the year 2001. Thirty six clinically healthy, cyclic and non-lactating thoroughbred mares belong to Shadai Corporation, Shiraoi Farm, Shiraoi 059-0901, Japan were assigned for this study. The animals ranged from 6-18 years old and weighed from 550-650 kg.Blood samples: Blood samples were collected from 9 mares out of 36 ones by jugular venipuncture into heparinised tubes starting from the day of ovulation then the animals were bled on every week for almost the first three months of pregnancy. Samples were centrifuged at 3,000 rpm for at least 15 min and plasma was harvested and stored at -20°C till assay.Radioimmunoassay: Pla...

Characterization of Immunoreactive IGF‐I Pattern During the Peri‐ovulatory Period of the Oestrous Cycle of Thoroughbred Mares and Its Relation to Other Hormones

“…Ir‐IGF‐I assay was carried out according to Hashizume et al. 1999, 2000 but using specific antibodies for horse (Derar et al. 2005, 2006).…”

“…Levels of immunoreactive (ir‐) inhibin, follicle stimulating hormone (FSH), LH, estradiol‐17β (E 2 ) and progesterone (P4) in peripheral blood were measured by RIA (Nambo et al. 1996a,b, 1998; Derar et al. 2005).…”

Immunoreactive Insulin-Like Growth Factor in Plasma during Pre- and Post-Partum Periods of Thoroughbred Mares from which the Newborn were Removed: its Pattern, Physiological Function and Relation to Other Hormones

“…Levels of immunoreactive (ir-) inhibin, follicle stimulating hormone (FSH), luteinizing hormone (LH), equine chorionic gonadotrophin (eCG), estradiol-17β (E 2 ) and progesterone (P 4 ) in peripheral blood were measured by RIA as described in previous papers [2,4].…”