Windmueller H G, Spaeth A E
Am J Physiol. 1981 Dec;241(6):E473-80. doi: 10.1152/ajpendo.1981.241.6.E473.
Previous work has demonstrated a continuous release of citrulline from the small intestine into the circulation. To evaluate the physiologic significance of this process, we have now measured citrulline uptake and release by isolated, perfused livers and, through surgical means and arteriovenous difference measurements, by various organs of the rat in vivo. Intestinally derived citrulline, an end product of glutamine nitrogen metabolism, passes through the liver without appreciable uptake. No significant extraintestinal source of circulating citrulline was found. Contrary to earlier suggestions, the liver releases no citrulline normally, but only when supplied with unphysiological high levels of ornithine and ammonia. Renal citrulline uptake was equivalent to approximately 83% the rate of intestinal release; kidneys, in turn, released arginine equivalent to approximately 75% of the citrulline taken up. Acute experiments in which the intestine, intestine plus liver, or kidneys were excluded from the circulation indicate that additional organs may also participate in citrulline exchange, at least when the circulating citrulline level is abnormal. The intestinal-renal pathway seems to account for a large though still unmeasured portion of the citrulline turnover in the circulation.
先前的研究表明，小肠中的瓜氨酸会持续释放到循环系统中。为了评估这一过程的生理意义，我们现在通过离体灌注肝脏来测量瓜氨酸的摄取和释放，并通过手术方法和动静脉差值测量，来测量大鼠体内各个器官的情况。肠道来源的瓜氨酸是谷氨酰胺氮代谢的终产物，它在通过肝脏时不会被大量摄取。未发现循环瓜氨酸有明显的肠外来源。与早期的观点相反，正常情况下肝脏不会释放瓜氨酸，只有在供给非生理性高水平的鸟氨酸和氨时才会释放。肾脏对瓜氨酸的摄取量约相当于肠道释放速率的83%；反过来，肾脏释放的精氨酸约相当于摄取瓜氨酸量的75%。在急性实验中，将肠道、肠道加肝脏或肾脏排除在循环之外，结果表明，至少在循环瓜氨酸水平异常时，其他器官也可能参与瓜氨酸的交换。肠-肾途径似乎在循环中瓜氨酸周转中占了很大一部分，尽管这一比例仍未测定。
