Comp. B&hem. Physiol. Vol. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 106A, No. 4, pp. 743-147, 1993 Printed in Great Britain 0300-9629/93 $6.00 + 0.00 10 1993 Pergamon zyxwvutsrqpo Press Ltd EFFECTS OF RECOMBINANT SALMON GROWTH HORMONE ON HYPOPHYSECTOMIZED MALE zyxwvutsrqponmlkjihgfe FUNDULUS HETEROCLITUS KENNETH OLmrRA,*t ROBERT W. GRIFFITH,* JOHN J. STEGEMAN,~ SHUNSUKEMORIYAMA$ and HIROSHI KAWAUCHI$ *Department of Biology, University of Massachusetts Dartmouth, North Dartmouth, MA 02747, U.S.A. (Tel: 508-999-8000); SDepartment of Biology, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, U.S.A.; §Laboratory of Molecular Endocrinology, School of Fisheries Sciences, Kitasato University, Sanriku, Iwate 022-O 1, Japan (Received 12 January 1993; accepted 17 February 1993) Abstract-l. Recombinant salmon growth hormone at doses of 0.8 and 2.1 pg/g significantly enhanced linear growth in hypophysectomized male killifish, Fundulus heteroclitus, over that of controls and a significant regression was found between growth and the logarithm of dose. 2. Bovine growth hormone elicited significant growth enhancement at all three dosages tested (1,4 and 10 pg/g) and a significant log/dose relationship was also observed. 3. Observations on the relative weight of the gonads indicate that whole salmon pituitary extract (25 pg/g) possesses strong gonadotropic activity and that both bGH and rsGH had smaller but significant effects on the gonads. 4. It is suggested that growth hormone may play a subsidiary synergistic role to other pituitary hormones in gonadal development. INTRODUCTION The primary ascribed function of growth hormone (GH) in fish, as in other vertebrates, is promotion of somatic growth (Ball, 1969). GH is also associated with several metabolic actions which appear to aid its growth-promoting role such as increased appetite (Pickford and Atz, 1957), conversion of food and protein (Markert et al., 1977) and nitrogen retention (Donaldson et al., 1979). There is also some evidence that GH plays a role in fish reproduction. Mam- malian GHs stimulated ovarian growth in coho salmon (Higgs et al., 1976, 1977), increased steroido- genesis by ovarian follicles of amago salmon (Young et al., 1983) and restored testicular 3/?-hydroxysteroid dehydrogenase in hypophysectomized (hypox) kil- lifish (Pickford et al., 1972). However, since the purified mammalian GHs used in these studies may have had trace contamination with pituitary go- nadotropic hormones (Pickford et al., 1972), it is difficult to interpret these reports of gonad stimu- latory actions. Recently Singh et al. (1988) observed that recombi- nant chum salmon growth hormone (rsGH) en- hanced in vivo and in vitro gonadal steroidogenesis in hypox male and female killifish, Fundulusheterocfitus. This recombinant hormone was synthesized by E. coli from salmon GH cDNA (Sekine et al., 1985) and was obviously free of contamination by pituitary gonado- TCurrent address: Department of Zoology, University of Rhode Island, Kingston, RI 02881, U.S.A. tropins. Enhancement of gonadal steroidogenesis by recombinant salmonid GH has recently been reported in goldfish as well (Van Der Kraak et al., 1990). Thus it would seem that GH’s gonadal steroidogenic effects in fish are real and not an artifact of contamination by other pituitary hormones. However, although rsGH has been shown to enhance growth in rainbow trout (Kawauchi et al., 1986), its ability to promote growth in killifish has not been assessed. Conse- quently, the observed steroidogenic responses in Fun - dulus may have been pharmacological and unrelated to this foreign hormone’s somatotrophic activity. In the present study we have tested the ability of rsGH at a series of doses to stimulate linear growth in hypophysectomized (hypox) killifish to see whether it is somatotrophic in this species. Because of the classic studies of Grace Pickford (Pickford, 1953a,b, 1954, 1959; Pickford et al., 1959) the killifish, Fun- dulus heteroclitus, is a standard test animal for the assay of growth hormone activity in teleost fishes. We also ran comparable tests using bovine growth hor- mone so that our data on rsGH could be compared with the extensive studies of Pickford. Since we were interested in the reported steroidogenic effects of rsGH we also measured the relative weight of the gonads (GSI). MATERIALS AND METHODS Adult male killifish (3.0-9.4 g) were collected in October 1988 by minnow trap and seine in South Dartmouth, MA. Prior to surgery, fish were accli- 743