Measurement of Adiponectin in Lactating Dairy Cows And Adiponectin, Insulin, NEFA, and Glucagon concentrations during an IVGTT and an IVIT in Lactating vs. Non-lactating Holstein Cows

Abstract

Adipose tissue is now known to be part of the endocrine system as well as an energy storage depot. One of the recently discovered adipose-secreted hormones is adiponectin. In many species, adiponectin concentrations are negatively correlated with adiposity and adiponectin has been reported to increase tissue sensitivity to insulin. No report of adiponectin secretion in cattle or any ruminant species could be found. In this study, weekly blood samples were taken from Holstein cows (n = 26) over the first 11 weeks of lactation. Plasma adiponectin, insulin and progesterone concentrations were determined and body condition score and milk production data were recorded. Adiponectin concentrations increased from 8.3 1.4 ng⁄ml in the first week to 16.0 2.7 ng&38260;ml at week 4 postpartum and then declined to remain at 12-13 ng⁄ml for the remainder of the study. Individual cows had consistently high or low adiponectin concentrations. Adiponectin concentrations did not correlate with body condition score, energy-corrected milk yield, lactation number, or progesterone (time to first cycle). Insulin concentrations increased from 4.70 ± 4.79 μIU⁄ml in the first week to 12.35 ± 10.38 μIU⁄ml at week 4. After week 4, insulin concentrations remained at 11-15 μIU⁄ml for the duration of the study. Within individual cows, insulin showed a -0.22 correlation with adiponectin (p = 0.12). A commercially available human adiponectin kit (HADP-61 HK, Linco, Millipore) was used to measure plasma adiponectin concentrations. Dilution of plasma as recommended by the manufacturer resulted in samples being below the sensitivity of the assay. Using undiluted plasma, adiponectin concentrations ranged from 0-80 ng⁄ml whereas in other species, concentrations are reported to be in the μg⁄ml range. Similarly, samples collected from growing bulls were undetectable when diluted, but were in the 0-40 ng⁄ml range when assayed undiluted. Some equine samples were assayed along with the bovine samples and after dilution (1:500) were in the ng⁄ml range. After adjusting the equine samples for dilution, a similar range (1-2 μg⁄ml) as reported for horses in the literature was attained. It is uncertain if the human adiponectin kit is able to accurately quantify bovine adiponectin concentrations, but our assays indicate that it is adequate for measuring trends.

Abstract II Insulin is a key metabolic hormone in ruminant and non-ruminant animals (Hart et al., 1979). The hypoinsulinemia of early lactation is part of a series of coordinated changes that occur around the time of parturition in support of lactation. Low plasma insulin concentrations reduce glucose uptake by insulin-responsive tissues (adipose and muscle) and facilitate greater uptake by the mammary gland, a tissue that is not insulin-responsive (Bauman & Elliot, 1983). The insulin-sensitizing effects of the adipose-secreted hormone, adiponectin were discovered in 2001, and have since been well described in humans and rodents, but very little is known about adiponectin in cattle. In a preliminary study, it was determined that adiponectin is measurable in bovine plasma using a commercially available radioimmunoassay (RIA) kit (HADP-61 HK, Linco, Millipore). In the present study, Holstein cows (n = 4) were administered an intravenous glucose tolerance test (IVGTT) and an intravenous insulin tolerance test (IVITT) at 45.3± 3.3 days prepartum and 19.5±3.2 days postpartum. Blood samples were taken at -30, -15, 0, 5, 10, 15, 20, 30, 45, 60, 90, 120 and 150 minutes relative to glucose or insulin infusion. Plasma glucose, insulin and adiponectin, and serum non-esterified fatty acid (NEFA) and glucagon concentrations were measured and analyzed. There was no difference between pre and postpartum glucose time to return to baseline, following the infusion of 0.25g of glucose⁄kg body weight (BW), but prepartum insulin concentrations rose higher (p < 0.0001), and took longer to return to baseline levels (p < 0.0041) than postpartum insulin. Adiponectin, NEFA, and Glucagon concentrations were unaffected by the IVGTT. The insulin dose of 0.1 IU⁄kg BW did not result in the expected decline in circulating glucose, nor did it have an effect on any of the other hormones. Adiponectin concentrations were significantly higher in prepartum cows than in postpartum cows (p < 0.0001), and individual variability between animals was observed, similar to what was seen in the preliminary study. There was no difference between pre and postpartum serum NEFA or glucagon concentrations. The lesser rise in, and accelerated time it took for insulin concentrations to return to pre-injection levels during the postpartum IVGTT indicates alterations in the glucose-insulin dynamics in postpartum cows. The large difference between pre and postpartum adiponectin concentrations suggests that low adiponectin levels help facilitate postpartum insulin resistance which increases the supply of glucose to the mammary gland, and aids in the metabolic support of lactation.