Abstract
Summary
The changes in body weight and serum levels of growth hormone (GH), so-matomedin insulin-like growth factor (IGF), and its carrier protein (CP) have been followed in rats from fetal to adult life. The weight gain was maximal (6.0 g/day) between Days 28 and 55 and minimal (1.4 g/day) between Days 79 and 120. Two distinct peaks of GH concentration have been found in normally growing animals. The first (mean ± SEM) was observed on the first day of life (371 ± 37 ng/ml) while the second peak (365 ± 97 ng/ml) coincided with an acceleration in growth rate beginning Day 40. An unexpectedly high fetal IGF level (812 ± 164 μU/ ml) rapidly declined to a nadir (189 ± 26 μU/ ml) at Day 21, and then rose gradually to a level of 572 ± 12 μU/ml on Day 120. The pattern of IGF CP concentration resembled that of weight gain rather than those of serum GH and IGF. The sex of animal appeared to have no influence on any component of growth-promoting system.
The administration of indomethacin (10 mg/kg) to pregnant animals inhibited the elevation not only of prostaglandins in maternal (99 ± 5 vs 235 ± 29 pg/ml) and fetal (398 ± 152 vs 913 ± 42 pg/ml) circulations, but also of GH (50 ± 5 vs 89 ± 5 ng/ml, and 83 ± 7 vs 137 ± 21 ng/ml, respectively).
In contrast, serum IGF levels in indometh-acin-treated pregnant rats were slightly but significantly elevated above those found in control animals throughout gestation. An unexplained dramatic decrease in IGF CP concentrations was observed in both groups of pregnant rats.
This study of the growth-promoting system in growing rats demonstrates its complexity and age dependency. Pregnancy is accompanied by significant and specific changes in all major components of the growth-promoting system. Some of these alterations may be related to elevated levels of PGs while the reasons for the others are still unknown.
Get full access to this article
View all access options for this article.