Maternal treatment with somatotropin during early gestation affects basic events of myogenesis in pigs

Abstract

The effects of maternal treatment with somatotropin during early gestation on fetal muscle development were determined. Crossbred gilts received daily injections of either 3 ml of a placebo ( n=31) or of 6 mg porcine somatotropin ( n=31) from day (d) 10 to 27 of gestation and samples were collected from d 28 embryos, d 37 and 62 fetuses, and from neonates. Administration of somatotropin increased the total number of fibres (primary and secondary fibres) in neonatal semitendinosus muscle of middle- and low-weight littermates, whilst no increase was observed in psoas major muscle. Somatotropin induced increases in muscular protein concentration, creatine kinase activity, muscle fibre girth, as well as type II to type I fibre conversion which revealed an advanced degree of differentiation at birth. Treatment effects on prenatal development preceded these changes. Increased DNA concentrations at d 28 of gestation indicate stimulation of cellular proliferation during the embryonic stages. Thereafter, the withdrawal of somatotropin caused a transient delay of differentiation as indicated by lower protein concentrations and creatine kinase activity compared with controls at d 37 of gestation. This was compensated again at d 62, and the number of semitendinosus primary fibres was increased in middle-weight fetuses, whereas secondary or total fibre number did not yet differ. However, enhanced expression of Myf5 and MyoD indicates higher numbers of initially determined, proliferating myoblasts that may have contributed to increased formation of secondary fibres. In conclusion, maternal somatotropin is an influential factor in early pregnancy capable of affecting the basic events of myogenesis.

Key signalling factors and pathways in the molecular determination of skeletal muscle phenotype

“…Indeed, daily injections of growth hormone (GH) in the sow during early pregnancy has been shown to enhance foetal fibre number (Rehfeldt et al, 2001), an effect likely to be mediated by IGF-1. IGF-1 and -2 stimulate both muscle cell proliferation and differentiation through the interaction with the type 1 IGF receptor (IGF1R), insulin receptor exon 11-(IR-A) and insulin receptor exon11 þ (IR-B), all of which are transmembrane tyrosine kinase receptors (Denley et al, 2005).…”

Effects of liposomes containing exogenous recombinant porcine somatotropin on rats

“…The range of biological effects of PST is extraordinary and has been discussed previously (Rehfeldt et al, 2001). Early studies by Lary established that PST worked in pigs (Harrelll et al, 1996;Etherton, 2000).…”

Effects of GRF in early gestation on foetal development in Large White and Genex-Meishan gilts

“…The greater IGF-I concentrations in GM than in LW gilts was not reported in boars (Louveau et al 1991) or late-pregnant gilts (Farmer et al 2000), but was recently observed in gilts on day 34 of pregnancy (Farmer 2003). High circulating IGF-I concentrations have been described in obesity (Scacchi et al 1999) and were thought to be achieved via a stimulatory effect of leptin on ST release. Indeed, Guay et al (2001) reported greater concentrations of leptin in Meishan crossbred than LW crossbred gilts on day 25 of pregnancy, yet values in late-gestation need to be obtained.…”

“…Rehfeldt et al (2001b) reported that maternal treatment with ST in early gestation increased total fiber number in the semitendinosus muscle of neonates, but there was no increase in the psoas major muscle. The authors concluded that pST could be muscle-specific with regard to its ability to increase fiber number.…”