Seebacher Frank, Franklin Craig E
School of Biological Sciences A08, University of Sydney, Sydney, NSW 2006, Australia.
Proc Biol Sci. 2003 Aug 7;270 Suppl 1(Suppl 1):S50-3. doi: 10.1098/rsbl.2003.0007.
The effectiveness of behavioural thermoregulation in reptiles is amplified by cardiovascular responses, particularly by differential rates of heart beat in response to heating and cooling (heart-rate hysteresis). Heart-rate hysteresis is ecologically important in most lineages of ectothermic reptile, and we demonstrate that heart-rate hysteresis in the lizard Pogona vitticeps is mediated by prostaglandins. In a control treatment (administration of saline), heart rates during heating were significantly faster than during cooling at any given body temperature. When cyclooxygenase 1 and 2 enzymes were inhibited, heart rates during heating were not significantly different from those during cooling. Administration of agonists showed that thromboxane B(2) did not have a significant effect on heart rate, but prostacyclin and prostaglandin F(2alpha) caused a significant increase (3.5 and 13.6 beats min(-1), respectively) in heart rate compared with control treatments. We speculate that heart-rate hysteresis evolved as a thermoregulatory mechanism that may ultimately be controlled by neurally induced stimulation of nitric oxide production, or maybe via photolytically induced production of vitamin D.
爬行动物行为性体温调节的有效性通过心血管反应得以增强，尤其是通过对加热和冷却作出反应时不同的心率（心率滞后）。心率滞后在大多数变温爬行动物谱系中具有重要的生态学意义，并且我们证明鬃狮蜥的心率滞后是由前列腺素介导的。在对照处理（给予生理盐水）中，在任何给定体温下，加热期间的心率显著快于冷却期间的心率。当环氧化酶1和2被抑制时，加热期间的心率与冷却期间的心率无显著差异。激动剂给药显示血栓素B2对心率没有显著影响，但与对照处理相比，前列环素和前列腺素F2α分别使心率显著增加（分别为3.5次/分钟和13.6次/分钟）。我们推测心率滞后作为一种体温调节机制而进化，其最终可能由神经诱导的一氧化氮产生刺激所控制，或者可能通过光解诱导的维生素D产生来控制。
