The role of GH was examined using an antiserum to rat GH (anti-rGH). When administered to lactating rats on day 2 of lactation it was without effect, whereas bromocriptine markedly suppressed milk production, with no additional effect of combined treatment. On day 6 of lactation, treatment with anti-rGH was also without effect, whilst bromocriptine again suppressed milk production. Combined treatment, however, suppressed milk synthesis completely, suggesting that GH was capable of maintaining about 50% of normal milk yield in the absence of prolactin at day 6 of lactation. By day 14 of lactation, anti-rGH treatment alone was capable of decreasing milk yield by about 20%, and again milk secretion only stopped completely when GH and prolactin were suppressed. These data suggest that the role of GH in supporting lactation increases as lactation progresses. The effects of GH in stimulating growth and in increasing milk yield in ruminants have been proposed to be mediated via insulin-like growth factor-I (IGF-I). In rats treated with anti-rGH, both IGF-I and IGF-II were decreased in serum. The concentration of the major IGF-binding protein (IGFBP-3) was not, however, affected by inhibition of GH or prolactin individually, but was decreased in animals treated with bromocriptine and anti-rGH. In animals given both bromocriptine and anti-rGH, concurrent treatment with recombinant bovine GH maintained milk yield at 50% of control values and normalized serum IGF-I, IGF-II and IGFBP-3 concentrations. By contrast, concurrent treatment with IGF-I or IGF-II, despite normalizing their respective concentrations in serum, failed to affect milk yield.(ABSTRACT TRUNCATED AT 250 WORDS)

Young growing rats treated with an antiserum to adipocytes showed marked reductions in several adipose tissue depots but surprisingly demonstrated increased body weight gain. During the first 3 wk after treatment body weight gain increased by 17% with no effect on food intake, whereas during weeks 3-7 body weight gain increased by 40-50% and was accompanied by a 15% increase in food intake. These animals thus exhibited increased food conversion efficiencies (intake/gain) of approximately 15-20% for almost 2 mo. Subsequently, food intake and body weight gain returned to normal (although body weight remained elevated) up to 6 mo. By this time several fat depots were still reduced in size, although total (chemical) fat was identical in treated and control groups. These results suggest that 1) reduction of body fat depots can be achieved using antibodies to adipocytes, 2) compensatory increases in lean body mass can occur, and 3) total fat mass may be regulated.

A specific antiserum to rat GH (anti-rGH) raised in sheep was used in young male and lactating rats. In both models a group of rats was found which appeared to generate a low response (low responders) to the injected sheep immunoglobulin, and was characterized by the ability of the antiserum to cause inhibition of growth for more than 21 days in the male rats, and to abolish milk yield when prolactin concentrations were lowered in the females. In the groups which generated a high response to the anti-rGH (high responders), growth was retarded for only 2-3 days in male rats, with a moderate milk yield maintained in lactating animals. The low-response animals were found to have a significantly longer half-life for circulating anti-rGH, when compared with the high-response animals. After 21 days, in the age-matched male rats, levels of anti-rGH were undetectable in the high-responders, whereas the low-response animals, which were nearly 160 g lighter, still had approximately 4.5 ml anti-rGH/l in their circulation. This anti-rGH was still capable of neutralizing GH, as concentrations of insulin-like growth factor-I (IGF-I) were 13.6 +/- 3.5 (mean +/- S.E.M.) and 76.9 +/- 2.0 nmol/l in the low-response and high-response groups respectively. The reason for these differences would appear to be that the immune response mounted by these low-response animals to the exogenous sheep immunoglobulin (i.e. rat anti-sheep) 7 days after treatment was less than 10% of that seen in the high-response group.(ABSTRACT TRUNCATED AT 250 WORDS)