Abstract
The problem of stress hyperglycaemia has been recognised in both human and veterinary medicine for many years. Among the domestic species we commonly deal with, cats appear particularly predisposed to develop this condition. The major problem this causes is in the diagnosis of diabetes mellitus. The finding of hyperglycaemia, even marked hyperglycaemia with concomitant glucosuria, is not diagnostic of diabetes mellitus in this species, even in the presence of appropriate clinical signs. Other diseases can clearly mimic the clinical picture seen with diabetes mellitus, cats suffering with stress hyperglycaemia can certainly have blood glucose concentrations well above the renal threshold, and in some cats this hyperglycaemia appears to be maintained for a few days. Demonstration of persistent hyperglycaemia is therefore required to make a diagnosis of diabetes, either through continued monitoring of the hyperglycaemic patient and/or through retrospective demonstration of hyperglycaemia (by the measurement of glycated haemoglobin or fructosamine concentrations). One of the curiosities of stress hyperglycaemia is the unpredictability of the phenomenon. Some cats which appear overtly ‘stressed’ have normoglycaemia, whereas others that appear ‘calm’ may develop severe hyperglycaemia. This may reflect the considerable challenge of the clinical and inevitably subjective assessment of ‘stress’, as well as inherent individual variations between cats. Despite the recognition of the feline predisposition to stress hyperglycaemia, until very recently there was very little data to suggest what causes this change. In the past, many clinicians have assumed that the counter-regulatory effect of ‘stress hormones’ such as catecholamines and glucocorticoids may induce peripheral insulin resistance and thereby cause the hyperglycaemia, but this phenomenon has now been the subject of some direct investigations by Drs Feldhahn, Rand and Kinnaird of the University of Sydney in Australia. They report some of their findings in this issue of the Journal of Feline Medicine and Surgery, and in a well conducted study they were able to show that the magnitude of stress hyperglycaemia does indeed vary between individuals that receive an identical acute ‘stressor’. However, when this phenomenon was observed, there appeared to be no change in the insulin sensitivity of the cats after the stressor compared to before the stressor. This suggests that if insulin resistance is the cause of the hyperglycaemia it must be a very transient change or, more likely, that another mechanism is responsible for the hyperglycaemia observed. The authors further provide evidence to suggest that increased gluconeogenesis (presumably hepatic in origin) is in fact the source of the hyperglycaemia that was observed. This is a fascinating study, elucidating the pathophysiological mechanisms behind a common clinical problem.
From the same group in Australia, there is a second paper in this issue written by Drs Martin and Rand, examining the effect of diet on blood glucose levels in both healthy and diabetic cats. This study again addresses a common clinical problem – that of what diet and feeding regime we should recommend for diabetic cats. Using a variety of mainly commercial dry and tinned cat foods, the authors found no evidence of postprandial hyperglycaemia in either the healthy or diabetic cats. The findings of this study have important clinical implications. Based on the authors’ results, the feeding of meals to diabetic cats does not need to be timed to coincide with either the injection of insulin, or predicted trough blood glucose concentrations. Indeed, as the authors suggest, from a glucoregulatory perspective, diabetic cats can happily be fed a typical commercial diet ad libitum. Yet again we are reminded that cats are not small dogs!
As 1999 draws to an end, I would like to close by extending my thanks to everyone who has contributed so much to making this first year of JFMS publication such a success. I would like to thank all the authors who have submitted papers, the editorial board, the ESFM office staff, the publishers, and of course all the readers! To all of you, I trust you will have a very Happy Christmas, and a peaceful New Year!