Lefcourt A M, Bitman J, Wood D L, Akers R M
Agricultural Research Service, USDA, Livestock and Poultry Sciences Institute, Beltsville, MD 20705, USA.
Domest Anim Endocrinol. 1995 Jul;12(3):247-56. doi: 10.1016/0739-7240(95)00022-7.
To investigate possible circadian and ultradian periodicities for plasma growth hormone in lactating dairy cows, integrated 15-min blood samples taken sequentially over 48 hr from six cows were analyzed by radioimmunoassay. The cows were housed in an environmental chamber at 19 +/- 0.5 degree C, 50% relative humidity, and 16 hr of light and 8 hr of darkness (lights on at 0700 hr); fed daily at 0900 hr; and milked at 0800 and 2000 hr. Peripheral concentrations of growth hormone for all six cows exhibited sinusoidal circadian rhythms with average minima of 4.1 ng/ml at 1820 hr and maxima of 5.3 ng/ml at 0630 hr. Estimated periods of ultradian rhythms for individual cows by spectral analysis, peak identification, and fitting cosine functions using least squares were 71 to 83 min for all cows. No direct relationship between ultradian peaks and milking or feeding was apparent. In conclusion, a circadian rhythm and an ultradian rhythm with a period around 80 min are probably intrinsic to mechanisms regulating peripheral growth hormone concentrations in the lactating dairy cow.
为了研究泌乳奶牛血浆生长激素可能存在的昼夜节律和超日节律，对6头奶牛在48小时内每隔15分钟依次采集的综合血样进行放射免疫分析。奶牛饲养在环境舱内，温度为19±0.5摄氏度，相对湿度为50%，光照16小时，黑暗8小时（0700时开灯）；每天0900时喂食；0800时和2000时挤奶。所有6头奶牛的外周生长激素浓度均呈现正弦昼夜节律，平均最低值在1820时为4.1纳克/毫升，最高值在0630时为5.3纳克/毫升。通过频谱分析、峰值识别以及使用最小二乘法拟合余弦函数，对个体奶牛超日节律的估计周期在所有奶牛中为71至83分钟。超日峰值与挤奶或喂食之间没有明显的直接关系。总之，昼夜节律和周期约为80分钟的超日节律可能是泌乳奶牛外周生长激素浓度调节机制所固有的。
