Dairy cows experience selective reduction of the hepatic growth hormone receptor during the periparturient period

Abstract

At parturition, dairy cows experience a 70% reduction in plasma IGF-I. This reduction coincides with decreased abundance of GHR1A, the liver-specific transcript of the growth hormone receptor (GHR) gene, suggesting impaired growth hormone-dependent synthesis of IGF-I. It is not immediately obvious that the periparturient reduction in GHR1A is sufficient to reduce hepatic GHR abundance. This is because 50% of total GHR mRNA abundance in prepartum liver is accounted for by ubiquitously expressed transcripts which remain collectively unchanged at parturition. In addition, the possibility that parturition alters GHR expression in other growth hormone target tissue has not been examined. To address these questions, we measured GHR gene expression and GHR protein in liver and skeletal muscle of four dairy cows on days -35,+3 and+56 (relative to parturition on day 0). Hepatic GHR abundance and GHR1A transcripts were lower on day+3 than on day -35 and returned to late pregnancy value by day+56. Additional studies in two other groups of cows indicated that the hepatic levels of the GHR protein recovered substantially within 10 days after parturition. These changes occurred without variation in the abundance of HNF4, a liver-enriched transcription factor activating the promoter responsible for GHR1A synthesis. In contrast to liver, levels of GHR gene expression and GHR protein were identical on days -35,+3 and+56 in skeletal muscle. These data suggest a role for the GHR in regulating tissue-specific changes in growth hormone responsiveness in periparturient dairy cows.

Modulation of the Somatotropic Axis in Periparturient Dairy Cows

“…Regarding GHR regulation, hepatic GHR1A transcript of dairy cows changes dramatically before and after partutition (Lucy et al, 2001; Kim et al, 2004). The hepatic abundance of GHR1A transcript is lower on day +3 than on day −35 and returns to late pregnancy value by day +56 (Figure 3).…”

“…(A) IGF-I, GHR1A and GHR other mRNA were analyzed by RPA. (B) Total cellular proteins (total) and membrane protein (membrane) were analyzed by western blotting for the abundance of the GHR (adapted from Kim et al, 2004). …”

Sustentabilidad, Turismo y Educación TII

“…La disminución de STH-R ARNm 1A, se asoció con una disminución en la hormona esteroidea progesterona (P4) y un incremento en la hormona esteroidea 17 β-estradiol (E2), poco antes del parto. Wook Kim et al (2004) sugirieron que, durante el BEN propio del posparto temprano, se disminuye la expresión genética del receptor STH-R ARNm 1A, produciendo una disminución tanto en la síntesis del receptor hepático específico de STH, como en la producción del IGF-I.…”

Growth Hormone Signaling in the Regulation of Acid Labile Subunit

“…The transcription factor responsible for the ubiquitous activity of the P3 promoter remains to be identified. Kim et al (2004) have reported that the bovine hepatic GHR protein can be measured by immunoblotting for the first time and reduced GHR1A abundance is partly responsible for the decline of GHR protein abundance in periparturient liver. Moreover, insulin and feed restriction regulates the efficiency of GH signaling in liver and adipose tissue of dairy cows by acting as a rheostat of GHR synthesis (Rhoads et al, 2004;Rhoads et al, 2007).…”