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

586
Chapter | 18 Pituitary Function
TABLE 18-7 Concentrations of PRL in Plasma of Healthy Animals
Species (n) Condition Mean SEM ( μ g/liter) Reference
Dog (6) 1.5 weeks of lactation 86 19 ( Concannon et al. , 1978 )
Dog (6) 8–32 h prepartum 117 24 ( Concannon et al. , 1978 )
Dog (5) Ovariectomized females 7.9–11.5 ( Rutteman et al. , 1987 )
Dog (6) Females, early luteal phase 2.5 0.4 ( Kooistra and Okkens, 2002 )
Dog (6) Females, anestrous 2.0 0.1 ( Kooistra and Okkens , 2002 )
Dog (7) Females, anestrous
c
7.0 1.2 ( Corrada et al. , 2003 )
Dog (6) Females in estrous cycle
a
3.9 1.6 ( de Gier et al. , 2006 )
Dog (6) Females in midluteal phase
b
3.2 0.2 ( Lee et al. , 2006 )
Dog (65) Males 2.7 0.2 ( Corrada et al. ,2006)
Dog (8) Males
b
3.0 0.3 ( Koch et al. , 2006 )
Cat (8) Early gestation 7.0 0.3 ( Banks et al. , 1983 )
Cat (8) End of gestation 43.5 4.5 ( Banks et al. , 1983 )
Cat (8) 4 Weeks post partum 40.6 7.2 ( Banks et al. , 1983 )
Cow (5) Luteal phase 23.3 4.8 ( Dieleman et al. , 1986 )
Cow (5) Follicular phase 15.8 2.7 ( Dieleman et al. , 1986 )
Sow (3) 2nd Week of lactation
c
9.1 1.4–26.1 5.0 ( Bevers et al. , 1978 ; Matthews and Parrott, 1992 )
Sow (3) Piglets removed 1.4 0.3–1.9 0.1 c ( Bevers et al. , 1978 ; Matthews and Parrott, 1992 )
Sheep (8) Males 68 15.3 ( Matthews and Parrott, 1992 )
a
Mean of 3 measurements/24 h during early follicular phase, six measurements/24 h during late follicular phase, and 6 measurements/24h during early luteal phase.
b
Mean of 24 measurements at 15-min intervals.
c
Mean of 8 measurements at 15-min intervals.
with dopaminergic drugs. These drugs are nevertheless
often used, the main application being in a physiological
condition in the bitch called pseudopregnancy ( Janssens,
1981 ). Administration of the dopamine agonist bromocriptine
results in rapid disappearance of the signs, suggesting
impending parturition. As treatment with bromocriptine
lowers PRL concentrations in plasma ( Okkens et al. , 1985 ;
Stolp et al. , 1986 ), it is likely that the lactation and maternal
behavior of the diestrual bitch is PRL dependent.
Isolated PRL deficiency has been reported in few case
reports in women that became apparent because these women
suffered from galactogenesis after normal pregnancies ( Douchi
et al. , 2001 ). However, the involvement of a genetic defect in
the observed PRL deficiency was not addressed. Isolated
PRL deficiency in domestic animals has not been reported.
f . Tests
Despite the variations in amino acid sequences of PRLs
from different species, plasma concentrations can be measured
in heterologous assays, for example, employing
labeled porcine PRL with an antibody against ovine PRL in
an assay for canine PRL ( Stolp et al. , 1986 ). PRL levels in
the blood may vary during the reproductive cycle, but the
basal levels in both male ( Meij et al. , 1996a ) and anestrous
female dogs are within similar narrow limits ( Stolp et al.
1986 ). Reference values are presented in Table 18-7 .
When there is a suspicion of prolactin deficiency, the
secretory capacity can be tested with TRH. In healthy dogs
intravenous administration of 10 μ g TRH per kg body
weight resulted in a mean plasma PRL peak level of 19.7
5.8 μ g/liter at 5 min following single TRH administration
and of 28.5 6.8 μ g/liter at 5 min following combined
administration of four hypothalamic-releasing hormones
( Meij et al. , 1996a ). In cats, 75 μ g TRH caused PRL elevation
to seven times the basal levels ( Banks et al. , 1983 ).
Prolactin concentrations can be suppressed with the dopamine
agonist bromocriptine. Both 20 μ g/kg intravenously
( Stolp et al. , 1986 ) and 10 μ g/kg orally ( Rijnberk et al. ,
1987 ) resulted in protracted decreases lasting at least 8 h
after administration.
III . NEUROHYPOPHYSIS
A . Vasopressin
1 . Gene Expression
Although there is considerable homology between the genes
for vasopressin (VP) and oxytocin (OT), each of the relevant