Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

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Chapter | 18 Pituitary Function
TABLE 18-6 Basal GH and IGF-I Concentrations in Plasma of Healthy Animals
Hormone
(Unit)
Species (n) Breed, Age Mean SEM
(Range)
Reference
GH Dog (63) Adult 1.9 0.1 ( Eigenmann and Eigenmann, 1981 )
( μ g/liter) Dog (6) Great Dane, 6 weeks 9.0 2.1 ( Favier et al. , 2001 )
Dog (6) Great Dane, 24 weeks 4.6 1.1 ( Favier et al. , 2001 )
Dog (6) Beagle (anestrus) 0.5 0.1 ( Selman et al. , 1991 )
Dog (6) Beagle (metestrus) 2.2 0.4 ( Selman et al. , 1991 )
Cat (25) Adult 3.2 0.7 ( Eigenmann et al. , 1984c )
Mare (12) Selle Français, 3–15yr 1.1 0.1 ( Davicco et al. , 1994 )
Cattle (4) Holstein steer 6.3 1.4 ( Lee et al. , 2005 )
Pig (4) 5 days 9.0 1.4 ( Lee et al. ,1993)
Pig (4) 170 days 1.5 0.1 ( Lee et al. , 1993 )
Sheep (7) MRHead, male adult 1.9 0.4 ( Viguie et al. , 2004 )
Sheep (30) East Frisian, 60 days 154 16 ( Altmann et al. , 2006 )
IGF-I Dog (8) Cocker spaniel, adult 36 27 ( Eigenmann et al. , 1984b )
( μ g/liter) Dog (10) Beagle, adult 87 33 ( Eigenmann et al. , 1984b )
Dog (10) Keeshond, adult 117 34 ( Eigenmann et al. , 1984b )
Dog (13) German shepherd, adult 280 23 ( Eigenmann et al. , 1984b )
Dog (6) Beagle, 24 weeks 237 52 ( Favier et al. , 2001 )
Dog (6) Great Dane, 24 weeks 307 31 ( Favier et al. , 2001 )
Cat (18) 2–19 year (196–791) ( Reusch et al. , 2006 )
Mare (12) Selle Francais, 7–11yr (154–318) ( Davicco et al. , 1994 )
Cattle (4) Holstein steer 133 18 ( Lee et al. , 2005 )
Pig (4) 170 days 182 30 ( Lee et al. ,1993)
Sheep (7) MRH, male adult 133 23 ( Viguie et al. , 2004 )
Sheep (30) East Frisian, 60 days 625 33 ( Altmann et al. , 2006 )
IGF-II Dog (8) Beagle, 24 weeks 152 13 ( Favier et al. , 2001 )
( μ g/liter) Dog (6) Great Dane, 24 weeks 171 13 ( Favier et al. , 2001 )
Pig (4) 170 days 326 19 ( Lee et al. ,1993)
The values can be converted to SI units:1 μ g GH/liter 0.0455 nmol/l; 1 μ g IGF/liter 0.133 nmol/liter.
pregnancy in the dog. Synthetic progestins or endogenous
progesterone may induce hyperplastic ductular changes in
the canine mammary gland with foci of immunoreactive
GH-producing cells ( Selman et al. , 1994b ). The MPAinduced
elevated plasma GH concentrations can be effectively
lowered by treatment with the progesterone receptor
antagonist aglepristone ( Bhatti et al. , 2006a ). Also canine,
feline, and human mammary carcinomas may express GH
mRNA within tumor tissue ( Mol et al. , 1995b, 1999 ). The
GH excess is, next to the acromegalic features and insulin
resistance, associated with the development of cystic endometrial
hyperplasia (CEH), which does not necessarily
have to originate within the mammary gland ( Bhatti et al. ,
2007 ). Local production of GH has also been documented
in canine insulinomas ( Robben et al. , 2002 ), in
normal growth plates, and in spontaneous osteosarcoma
( Kirpensteijn et al. , 2002 ). Enhanced expression of GHR
mRNA in duodenal and colonic biopsies of dogs with
chronic enteropathies ( Spichiger et al. , 2005 ) and distraction-induced
osteogenesis ( Theyse et al. , 2006 ) points to a
role for GH in gastrointestinal and bone repair processes.
In cats, excessive amounts of GH may be secreted by
a pituitary tumor resulting in acromegalic features and
insulin resistance ( Hurty and Flatland, 2005 ). In untreated
diabetic cats without concurrent hypersomatotropism,
plasma IGF-I concentrations are lower in comparison to
control animals, whereas in case of underlying excessive
GH secretion, plasma IGF-I concentrations are elevated
( Reusch et al. , 2006 ).
g . Tests
As GH secretion is pulsatile, single values are of no great
diagnostic value. In healthy individuals, basal plasma GH
concentrations ( Table 18-6 ) may be very low. Hence, when
GH deficiency is suspected, a stimulation test is needed.
In the dog stimulation with clonidine, xylazine, GHRH, or
ghrelin has proved to be reliable for this purpose, whereas
in calves and lambs GHRH stimulation has been used.
Elevated GH values are not definitive proof of acromegaly,
not only because of the pulsatile nature of the
GH secretion but also because environmental factors may
cause sharp increases. Although hypersecretion should be
checked by an inhibition test, in case of progestin-induced
GH secretion, a blunted stimulation of high basal GH concentrations
may support the diagnosis, together with elevated
plasma IGF-I concentrations ( Selman et al. , 1991 ).