Clenbuterol increases muscle fiber size and GATA‐2 protein in rat skeletal muscle in utero

Abstract

Certain beta(2)-adrenoceptor agonists, such as clenbuterol, are known to elicit a muscle-specific anabolism or hypertrophy in both normal and catabolic muscle in a wide variety of species. However, the underlying mechanism(s) of the beta(2)-agonist-induced anabolism remains unclear. This study aimed to determine the effects of clenbuterol administration in utero on skeletal muscle and to examine the underlying molecular mechanisms. Pregnant rats were fed clenbuterol (2 mg/kg diet) from Day 4 of gestation (4 dg) until weanling and fetal samples were taken from 13.5, 15.5, 17.5, and 19.5 dg and from 1d neonatal pups. Muscles were analyzed for total DNA, RNA and protein and sections examined morphologically for changes in muscle development. Western and immunohistochemical analyses were performed to identify changes in known myogenic signaling proteins. Clenbuterol increased the size of both fast and slow fibers in utero which was associated with a decreased DNA:protein ratio (28%) and an increased RNA:DNA ratio (36%). Additionally, drug treatment in utero induced a decrease in the fast:slow fiber ratio (38%). These myogenic changes were correlated with an increase in the GATA-2 hypertrophic transcription factor at both 17.5 dg (by 250%) and 19.5 dg (by 40%) in fetuses from clenbuterol treated dams. In addition, drug treatment resulted in increased membrane association of PKC-micro at 17.5 dg (325%) and increased PKC-alpha cytosolic abundance (40%) and PKC-theta membrane abundance at 19.5 dg (250%). These results are the first demonstration that beta(2)-agonists such as clenbuterol may act through upregulating the GATA-2 transcription factor and implicate certain PKC isoforms in the drug-induced regulation of skeletal muscle development.

Responses to maternal GH or ractopamine during early–mid pregnancy are similar in primiparous and multiparous pregnant pigs

“…63 gestation, term w150 days) did not increase weight or alter body composition of neonatal twin lambs, with the exception of increased heart weight (Shackelford et al 1995). Similarly in rats, fetal weight in late pregnancy and weight of neonatal pups were not changed by feeding pregnant dams the b 2 -adrenergic agonist clenbuterol from day 4 after mating and throughout pregnancy, although neonatal cardiac hypertrophy was also reported in this species (Maltin et al 1990, Downie et al 2008. Limited studies in women with suspected impaired fetal growth have also found no change in birth weight in response to short-term treatment with the b-adrenergic agonist ritodine in late pregnancy (Say et al 2001).…”

“…In lambs, in utero exposure to the b 2 -adrenergic agonist L 644,969 from day 25 to 95 of pregnancy also did not alter fiber type proportion or size in young adult offspring (Shackelford et al 1995). In contrast, feeding rats the b 2 -adrenergic agonist clenbuterol throughout most of pregnancy and through lactation increased muscle fiber size but decreased muscle weights and secondary:primary fiber ratios in fetuses (Maltin et al 1990, Downie et al 2008. This decreased muscle weight persisted postnatally, with a decrease in total fiber numbers (Maltin et al 1990).…”

Adverse Effects from Clenbuterol and Ractopamine on Nematode Caenorhabditis elegans and the Underlying Mechanism

“…Clenbuterol caused an impairment of collagen turnover by down-regulating MMP-9 activity [11]. Clenbuterol not only enhanced muscle fiber size but also increased expression of GATA-2 protein in skeletal muscle of rat uterus [12]. The preferential involvement of calpain 2 autolysis was found for clenbuterol-induced skeletal muscle remodelling in rats [13].…”

Novel role for β‐adrenergic signalling in skeletal muscle growth, development and regeneration

“…We have previously identified the β‐adrenergic signalling pathway as a potential novel regulator of skeletal muscle regeneration 4,5 . In addition, we and others have postulated a role for β‐adrenoceptors in skeletal muscle growth 6 and development 7 …”