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Title: LEPTIN AND LEPTIN RECEPTOR EXPRESSION IN SWINE TISSUES IN RESPONSE TO IN VIVO SOMATOTROPIN TREATMENT

Author
item Ramsay, Timothy
item Richards, Mark

Submitted to: American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 4/21/2005
Publication Date: 7/1/2005
Citation: Ramsay, T.G., Richards, M.P. 2005. Leptin and leptin receptor expression in swine tissues in response to in vivo somatotropin treatment [abstract]. Journal of Animal Science. 83(Supplement 1):25.

Interpretive Summary:

Technical Abstract: The present study examined the response of the leptin and leptin receptor genes to porcine somatotropin (pST) stimuli in finishing pigs. Twelve crossbred barrows (Yorkshire x Landrace) were individually fed a diet containing 18% CP, 1.2% lysine, and 3.5 Mcal of DE/kg ad libitum. At 90 kg, six randomly selected pigs were treated with daily injections of recombinant pST, (10 mg). The other six pigs were injected with bicarbonate buffer (controls). With initiation of pST treatment, the amount of feed offered was at 85% of calculated ad libitum intake, based upon BW and adjusted every 3 d. Diet restriction was performed to correct for the known inhibition in feed intake due to pST treatment in swine. Animals were maintained on treatment for 2 wk with a blood sample obtained on d14. Tissue samples were collected on d15, frozen in liquid nitrogen and stored at -80ºC prior to analysis for gene expression by RT-PCR and transcript quantification by capillary electrophoresis with laser-induced fluorescence detection. Samples included outer (OSQ) and middle subcutaneous adipose tissues, leaf fat, liver, latissimus dorsi and biceps femoris. Restricted feeding resulted in no change in bwt of control pigs while pST treatment increased bwt by 6.9 ± 0.5 kg (p < 0.001). Treatment with pST produced a twelve-fold increase in serum ST (p < 0.002). Serum leptin was elevated by 17% in swine treated with pST (p < 0.01). Leptin mRNA level was increased in liver by pST treatment (p < 0.05). Leptin receptor (Ob-Rb) expression was reduced 27% by pST administration in liver (p < 0.04) and by 49% in OSQ (p < 0.02) relative to control animals consuming equivalent amounts of feed. The present data suggest the effect of pST on leptin gene expression in ad libitum fed pigs is primarily the result of pST's inhibition of feed intake, since the restriction feeding regimen precluded detection of major change in leptin gene expression. Changes in leptin receptor expression by in vivo pST treatment suggests a change in sensitivity to leptin in liver and OSQ.