Ghrelin-stimulation test in the diagnosis of canine pituitary dwarfism

Abstract

This study investigated whether ghrelin, a potent releaser of growth hormone (GH) secretion, is a valuable tool in the diagnosis of canine pituitary dwarfism. The effect of intravenous administration of ghrelin on the release of GH and other adenohypophyseal hormones was investigated in German shepherd dogs with congenital combined pituitary hormone deficiency and in healthy Beagles.Analysis of the maximal increment (i.e. difference between pre-and maximal post-ghrelin plasma hormone concentration) indicated that the GH response was significantly lower in the dwarf dogs compared with the healthy dogs. In none of the pituitary dwarfs, the ghrelin-induced plasma GH concentration exceeded 5 lg/l at any time. However, this was also true for 3 healthy dogs. In all dogs, ghrelin administration did not affect the plasma concentrations of ACTH, cortisol, TSH, LH and PRL .Thus, while a ghrelin-induced plasma GH concentration above 5 lg/l excludes GH deficiency, false-negative results may occur.

Ghrelin affects the hypothalamus–pituitary–thyroid axis in humans by increasing free thyroxine and decreasing TSH in plasma

“…injection of ghrelin than after that of placebo after 20 min (16). But in studies on dogs (17,18) and humans (19,20), ghrelin did not change TSH levels. Also, the synthetic GHS-R agonist hexarelin was found to decrease TSH secretion after a single dose within 2 h (21).…”

“…However, most studies in animals and humans failed to detect an effect on the HPT axis possibly due to methodological limitations, e.g. lack of control condition (17)(18)(19)(20), insufficient sample size and measurement period (17). In addition, several pulses of ghrelin might be required to elicit a suppressive effect since ghrelin physiologically exhibits a pulsatile secretion pattern (61).…”

Disorders of Growth Hormone

“…Healthy dogs may at times have low to undetectable GH levels, because GH is secreted in pulses and GH may be very low between the normal pulses (Eigenmann, 1982b;Eigenmann et al, 1984d;Kooistra et al, 2000a;Bhatti et al, 2006c). Various studies showed that random basal GH concentrations of pituitary dwarfs overlap largely with those of healthy dogs.…”

“…Healthy dogs may at times have low to undetectable GH levels, because GH is secreted in pulses and GH may be very low between the normal pulses (Eigenmann, 1982b;Eigenmann et al, 1984d;Kooistra et al, 2000a;Bhatti et al, 2006c). Bhatti, et al (2006c) found basal GH levels in German Shepherd dwarfs to be between 0.4 to 1.2 μg/L (mean 0.7) and 0.2 to 1.0 μg/L (mean 0.6) in healthy Beagle dogs. In the study of Kooistra, et al (2000a), basal GH levels ranged between 0.3 to 1.5 μg/L (mean 0.5) in the German Shepherd dwarfs and between 0.6 to 5.2 μg/L (mean 1.8) in healthy Beagle dogs.…”

Evaluation and Diagnostic Potential of Serum Ghrelin in Feline Hypersomatotropism and Diabetes Mellitus

“…In humans, dogs and cats, the relationship between endogenous ghrelin secretion and pituitary GH secretion is not fully elucidated. 15,[30][31][32] Humans with acromegaly have lower ghrelin concentrations and these tend to increase after surgery in correlation with normalization of GH and IGF-I and improved insulin sensitivity, suggesting negative feedback to occur exerted by excess GH on ghrelin secretion. 10,12,33 Based on the before and after RT results of this study, this hypothesized negative feedback effect could also be present in the cat.…”