Single injection of clenbuterol into newly hatched chicks decreases abdominal fat pad weight in growing broiler chickens.

The aim of the current study was to examine the effects of clenbuterol injection into newly hatched chicks on both the abdominal fat pad tissue weight and the skeletal muscle weight during subsequent growth. Twenty-seven 1-day-old chicks were divided into two groups, receiving either a single intraperitoneal (i.p.) injection of clenbuterol (0.1 mg/kg body weight) or phosphate-buffered saline (PBS). Body weight gain, feed intake and feed conversion ratio were not affected by clenbuterol injection during the 5-week experimental period, while the abdominal fat pad tissue weight of the clenbuterol-injected chicks was lower than that of the control chicks at 5 weeks post-injection. Plasma non-esterified fatty acid concentrations were significantly increased in the clenbuterol-injected chicks, while plasma triacylglycerol concentrations did not differ. Additionally, the enzymatic activity of fatty acid synthase was lower in the liver of the clenbuterol-injected chicks. Conversely, the skeletal muscle weights were not affected by clenbuterol injection. These results suggest that a single clenbuterol injection into 1-day-old chicks decreases the abdominal fat pad tissue weight, but may not affect skeletal muscle weights during growth. © 2015 Japanese Society of Animal Science.

Single injection of the ß2-adrenergic receptor agonist, clenbuterol, into newly hatched chicks alters abdominal fat pad mass in growing birds.

Excessive energy is stored in white adipose tissue as triacylglycerols in birds as well as in mammals. Although ß2-adrenergic receptor agonists reduce adipose tissue mass in birds, the underlying mechanism remains unclear. The aim of the current study was to examine the effects of a single intraperitoneal injection of the ß2-adrenergic receptor agonist, clenbuterol, on the abdominal fat pad tissue development. Thirty-three chicks at 1-day-old were given a single intraperitoneal injection of clenbuterol (0.1mg/kg body weight) or phosphate-buffered saline. At 2 weeks post-dose, the weight of the abdominal fat tissue was decreased in the clenbuterol-injected chicks, and small adipocyte-like cells were observed in the abdominal fat pad tissue of the clenbuterol-injected chicks. Then, the expression of mRNAs encoding genes related to avian adipogenesis was examined in the abdominal fat pat tissue. The expression of mRNAs encoding Krüppel-like zinc finger transcription factor 5 (KLF-5), KLF-15, and zinc finger protein 423 in the abdominal fat pad tissue of the clenbuterol-injected chicks was significantly lower (P<0.05) than that of the control chicks, while the expression of mRNA encoding peroxisome proliferator-activated receptor-gamma was not affected. In addition, both mRNA expression (P<0.05) and enzymatic activity (P<0.05) of fatty acid synthase (FAS) were decreased in the abdominal fat pad tissue of the clenbuterol-injected chicks, while clenbuterol injection did not affect FAS activity in liver. These results suggested that a single injection with clenbuterol into newly hatched chicks reduces their abdominal fat pad mass possibly via disrupting adipocyte development during later growth stages.

The effects of intraperitoneal clenbuterol injection on protein degradation and myostatin expression differ between the sartorius and pectoral muscles of neonatal chicks.

The purpose of this study was to investigate the effects of injection of the ß2-adrenergic receptor agonist clenbuterol on the skeletal muscles of neonatal chicks (Gallus gallus domesticus). One-day-old chicks were randomly divided into four groups and given a single intraperitoneal injection of clenbuterol (0.01, 0.1, or 1mg/kg) or phosphate-buffered saline. Twenty-four hours after the injection, the sartorius muscles (which consist of both slow- and fast-twitch fibers) of chicks that received 0.01 or 0.1mg/kg clenbuterol were significantly heavier than those of controls, while there were no between-group differences in the weight of the pectoral muscles, which consist of only fast-twitch fibers. Muscle free N(t)-methylhistidine, regarded as an index of myofibrillar proteolysis, was decreased in the sartorius muscle of the clenbuterol-injected chicks, while it was not affected in the pectoral muscles. In the sartorius muscle of the clenbuterol-injected chicks, myostatin and atrogin-1/MAFbx mRNA expressions were decreased, while insulin-like growth factor-I was unaffected. These observations suggested, in 1-day-old chicks, clenbuterol might increase mass of the sartorius muscle by decreasing myostatin gene expression and protein degradation.