Volume loading hypoalgesia in SHR, WKY and F1 offspring of a SHR x WKY cross

The effects of volume loading on a nociceptive reflex, arterial blood pressure and heart rate were studied in spontaneously hypertensive rats (SHRs), Wistar Kyoto normotensive rats (WKYs) and the F1 offspring of a SHR x WKY cross. Volume loading resulted in significantly greater inhibition of the tail-flick reflex to painful radiant heat in SHRs compared to WKYs. The F1 offspring of a SHR x WKY cross showed levels of hypoalgesia to volume loading that were intermediate to those of SHRs and WKYs. There were no differences between these strains in their hypotensive and bradycardic responses to volume loading. These findings are discussed in terms of cardiovascular-somatosensory interactions.