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

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Chapter | 18 Pituitary Function
TABLE 18-3 Basal Concentrations of POMC-Derived Peptides in Plasma of Healthy Animals a
Hormone (Unit) Species (n) Sampling Time Mean SD (Range) Reference
ACTH Dog (160) 08.00–10.00 h (2.2–19.8) ( Peterson et al. , 1986 )
(pmol/l) Cat (130) After overnight fast 24 26 ( Javadi et al. ,2004)
Horse (10) 7 1 ( Orth et al, , 1982 )
Cattle (39) 08.00–14.00 h 0.6 0.04 ( Beerda et al. , 2004 )
Pig (11) Morning 2.4 0.5 ( Hari and Pliska, 2005 )
Sheep (male, 6) 15 2 ( Gardner et al. , 2006 )
Ferret (21) 14.30–16.00 (11.7–24.0) ( Schoemaker et al. , 2002a )
α -MSH Dog (160) 08.00–10.00 h (1.5 – 15) ( Peterson et al. , 1986 )
(pmol/l) Cat (130) After overnight fast 180 122 ( Javadi et al. , 2004 )
Horse (10) 14.4 1.2 ( Orth et al. , 1982 )
Ferret (44) 14.30–16.00 (4–108) ( Schoemaker et al. , 2002a )
β -END Dog (160) 08.00–10.00 h (1.5–17.4) ( Peterson et al. , 1986 )
(pmol/l) Horse (10) 18.3 4.4 ( Orth et al. , 1982 )
a
Most of the values have been converted to SI units, employing: 1 ng ACTH/liter 0.22 pmol/l; 1ng α -MSH/liter 0.60 pmol/l; 1ng β -END/
liter 0.29 pmol/l.
TABLE 18-4 Maximal Plasma Concentrations of POMC-Derived Peptides Following Intravenous Administration
of a Variety of Stimulants
Hormone (Unit) Species (n) Substance Dose Mean SEM Reference
ACTH Dog (8) CRH 1 μ g/kg 61 9 ( Meij et al., 1996a )
(pmol/l) Dog (6) AVP 0.6 μ g/kg 50 15 ( Kemppainen and Sartin, 1987 )
Dog (16) LVP 0.2 U/kg 49 5 ( van Wijk et al., 1994 )
Dog (19) Haloperidol 0.06 mg/kg 62 7 ( Rijnberk et al., 1987 )
Dog (6) Insulin 0.5 U/kg 85 20 ( Kemppainen and Sartin, 1987 )
Cat (6) CRH 1 μ g/kg 29 3 ( Willemse and Mol, 1994 )
Sheep (5) CRH 1 μ g/kg 125 52 ( Pradier et al., 1986 )
Sheep (5) AVP 1 μ g/kg 202 77 ( Pradier et al., 1986 )
Pig (4) CRH 1 μ g/kg 18 3 ( Hari and Pliska, 2005 )
α -MSH Dog (19) Haloperidol 0.06 mg/kg 40 4 ( Rijnberk et al., 1987 )
(pmol/l) Cat (6) CRH 1 μ g/kg No effect ( Willemse and Mol, 1994 )
Cat (4) Haloperidol 2 mg/kg 125 36 ( Peterson et al., 1994 )
et al. , 1997b ; Peterson et al. , 1986 ; Rijnberk et al. , 1987 )
with pituitary-dependent hyperadrenocorticism of IL origin.
In the horse, basal plasma ACTH concentration predicts
a pituitary adenoma of the IL with 100% sensitivity
( van der Kolk et al. , 1995 ).
Of the dynamic tests, the dexamethasone suppression
tests (see Chapter 19 on adrenocortical function) are
still the best for the diagnosis and differential diagnosis of
excessive ACTH and glucocorticoid secretion. In animals
suspected of having pituitary-adrenocortical insufficiency,
the secretory capacity for POMC-derived peptides can be
measured by provocative testing.
CRH and AVP are also used in the differentiation
between pituitary-dependent hyperadrenocorticism and
hyperadrenocorticism resulting from adrenocortical tumor.
The chronically suppressed corticotropic cells are presumed
to be unresponsive to these stimuli. However, Meijer et al. ,
(1978) found considerable overlap in plasma cortisol value
in the AVP test, whereas much less is claimed to occur in
the CRH test ( Peterson, 1986 ). It has been demonstrated that
LVP stimulates cortisol release by adrenal tumors in a direct
way ( van Wijk et al. , 1994 ).
It has been shown that dogs with pituitary-dependent
hyperadrenocorticism usually remain responsive to single
CRH administration ( Rijnberk et al. , 1987 ) or combined
hypophysiotropic stimulation in spite of persisting hypercortisolism
and neoplastic transformation of the corticotropes
( Meij et al. , 1997a ). The cells of the pituitary lesions
were found to be less responsive to CRH in vitro than were
normal corticotropes ( Mol et al. , 1987 ) and less sensitive
to inhibition by glucocorticoids ( van Wijk et al. , 1998 ).
As far as the possibility for manipulation of canine IL
function is concerned, of the substances tested only the
dopamine agonist haloperidol ( Kemppainen and Sartin,