Expression of lipolytic genes in the adipose tissue of pregnant and lactating Holstein dairy cattle.

The objective of this study was to determine the expression of beta-adrenergic receptors, hormone-sensitive lipase, and its cofactor perilipin in adipose tissue, and their relationships to rates of lipolysis and body fat use in Holstein dairy cattle during late pregnancy and lactation. Twenty Holstein dairy cattle were grouped by lactation number (1, 2, and 3 or more), and subcutaneous adipose tissue was sampled to measure lipolytic rates and gene expression. The 305-d mature-equivalent yields (305ME) for first, second, and third or higher parity cows were 13,220, 15,659, and 13,890 kg [standard error of the means (SEM) 931]. Milk fat and protein averaged 3.55 and 3.3%, across all parities. Milk production at 30 d in milk (DIM) was 30.7 kg/d (3.4) with 3.6% fat and 2.7% protein; and at 90 DIM was 47.5 kg/d (1.5) with 3.4% fat and 2.9% protein. Body weight and body condition score (BCS), measured at -30, 30, 90, and 270 DIM averaged 697, 605, 652, and 693 kg and 3.3, 2.4, 2.8, and 2.8 BCS units. Adipose tissue was extracted for RNA and tissue was incubated to measure basal and stimulated lipolysis. Basal lipolysis increased following parturition, and basal and stimulated lipolysis peaked at 90 DIM. The B1, B2, and B3 adrenergic receptors (AR) were expressed at all time points, as shown by PCR and agarose gel analysis as well as real-time reverse transcription-PCR. Expression of B1 AR, relative to that at d -30, increased 170, 72, and 112% at 30, 90, and 270 DIM. Expression of B2 AR increased 75, 121, and 100%; and that of B3 AR increased 111, 125, and 69%. Expression of hormone-sensitive lipase increased 180, 359, and 47% at the same time points. Expression of perilipin increased 227, 1,847, and 126%. The greatest expression of these 5 genes corresponded with the fastest rates of lipolysis at 90 DIM. This work demonstrates that an increase in the expression of beta-adrenergic receptors is part of the multifaceted regulation of lipolysis in dairy cattle.