Serum Levels of Insulin-Like Growth Factor-I, Thyroid Hormones and Skeletal Muscle Fiber Size in Castrated Lambs with and Without Androgen Treatment

Ismail Ismail

doi:10.3844/ajassp.2009.518.522

Abstract

Twelve, intact male lambs, 1-2- weeks old, were divided into 3 groups, Group W (4 lambs) were castrated at age less than 1 month, group WT (4 lambs) were castrated at the same age and treated with testosterone and group R (4 lambs) were left intact and served as control. Testosterone Propionate replacement was administered intramuscularly at a dose of 12.5 mg started at the day of castration and continued every 2 days for 21 days, then at a dose of 25 mg every 2 weeks until slaughter. Serum insulin-like growth factor-1, T3 and T4 concentrations were measured using ELISA. Lambs were slaughtered at 8 months of age and semitendinosus and splenius muscles fiber areas were measured using digital image technique. In WT and R groups, IGF-I concentrations were significantly higher (p<0.05) at 4 and 8 months compared to IGF-I levels in group W. Serum T3 concentrations were significantly lowest in group R compared to groups W and WT. Serum levels of T4 were not significantly affected by age in younger lambs, although it was significantly higher in group R at 6 and 8 months of age. In group R, splenius muscle fiber area (1458±193 um 2 ) was significantly higher (p<0.05) than that of groups W and WT while the muscle fiber area of the semitendinosus muscle was not significantly different among all groups.

Highlights

Growth have been found to be influenced by many endocrine hormones such as androgens, growth hormone (GH), Insulin, Insulin-like Growth Factors (IGFs) and thyroid hormones[8]
It was found that myostatin expression in muscles of intact males is lower than females and castrated animals
Histological processing of the muscle tissue samples was performed using (Histokinette Processor Leica, Germany), after tissue fixation completed they were transferred to be embedded in blocks of paraffin and when the blocks were ready 5 μm tissue sections using microtome (Biocut Leica, Germany).The sections were transferred on microslides and left to dry

Summary

Introduction

Growth have been found to be influenced by many endocrine hormones such as androgens, growth hormone (GH), Insulin, Insulin-like Growth Factors (IGFs) and thyroid hormones[8]. It has been found that male animals possess greater muscle in the neck and forequarters than females and that intact male grow faster, utilize feed more efficiently and have less fat per carcass than castrated males and females[2,10]. This sexual dimorphism is attributed to the presence of androgens, IGF-1 and GH[8]. Studies have shown that T3 stimulates transcription of myogenic genes and induces differentiation of myoblasts[5] On turn, these effects may direct or involve alterations in the local production of growth factors such as IGF-I and IGF-II[5]. It has been found that T4 potentiates growth hormone action in many tissues and is responsible for increased musclization in callipyge sheep[11]

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