Introduction

The central role that growth hormone (GH) plays in growth and body composition has been documented extensively but in more recent times its role in a wide variety of functions, particularly in terms of reproduction and immune response, has begun to be explored more fully. In this chapter we describe the use of a model of GH deficiency involving passive immunization of rats with a specific antiserum to rat GH (anti-rGH) to investigate various aspects of development. The data provide evidence that GH plays a central role in development of both reproductive and immune functions in vivo, as well as demonstrating that GH plays a paradoxical role in stimulating adipocyte differentiation whilst enhancing lipid mobilization from mature adipocytes. Finally we describe the important autocrine/paracrine role that GH plays in the development of pituitary somatotrophs and its ability to sensitize the thyroid and ovary to the actions of TSH and the gonadotrophins, respectively.

Production and characterization of antibodies to rGH

Antisera to rGH were produced in sheep using a highly purified rGH preparation as immunogen. When examined in a radioimmunoassay, using 125I-rGH, cross-reactivity with other pituitary hormones was very low and could be explained in terms of their contamination with rGH (Madon et al., 1986). When the antiserum was assessed in vitro at the concentrations which could be achieved in vivo, it was capable of binding in excess of 1000 ng/ml of rGH. Since GH concentrations in the female rats used in this study are typically 100 ng/ml or lower, this indicated that the anti-rGH would effectively neutralize GH in vivo at the doses used.