Abstract
The effects of dietary saturated and polyunsaturated fatty acids (PUFAs) of the n-3 and n-6 series on avian pituitary sensitivity were investigated by infusing human growth hormone (GH) releasing hormone--fragment 1-29--and chicken luteinising hormone releasing hormone (LHRH) into catheterized broiler chickens. At 3 weeks of age three groups (n = 18; six birds per group) were fed for 6 weeks isonitrogenous and isoenergetic experimental diets containing 80 g/kg of edible tallow (saturated fatty acids), fish oil (n-3 PUFAs) or sunflower oil (n-6 PUFAs). Jugular catheterisation was performed under general anaesthesia during week four of the dietary treatments and the birds allowed 7 days post surgery to recover. A bolus of LHRH (20 microg/bird) and a GH releasing hormone (12.5 microg/kg) infusion was given on different days to each chicken and serial blood samples taken over a 1 h period. Plasma luteinising hormone and GH concentrations were measured by radioimmunoassay. Pre-infusion GH concentrations were similar for the tallow, fish and sunflower oil dietary groups (5.2 +/- 3.9, 5.2 +/- 1.0 and 6.1 +/- 3.1 ng/ml, respectively), however, GH concentration in response to the GH releasing hormone infusion was elevated in the sunflower oil group (44.7 +/- 5.7 ng/ml) when compared to chicken fed tallow (33.7 +/- 9.7ng/ml) or fish oil (21.3 +/- 5.0 ng/ml). There was a significant decrease (P < 0.05) in the clearance rate of plasma GH for the birds fed the fish oil compared with those fed sunflower oil with an intermediate value being observed in the tallow fed group. Pre-infusion plasma luteinising hormone concentrations for the birds fed tallow (3.2 +/- 0.7 ng/ml) were significantly elevated (P < 0.05) when compared to birds fed either the sunflower oil (0.84 +/- 0.25 ng.ml) or fish oil (0.93 +/- 0.22 ng/ml) diets. There were no significant differences between the dietary groups in either the maximal plasma luteinising concentration or its disappearance rate following the LHRH infusion. The data demonstrate that dietary fatty acids alter avian pituitary sensitivity and this modulation is determined by the nature of the dietary fat rather than the degree of saturation per se. In addition, this study also shows that dietary fats have a differential effect on pituitary cell activity and are specific to certain pituitary cell types.