C. Gobello et al., Twenty-four-hour profiles of serum prolactin and luteinizing hormone in anoestrous crossbred bitches, REPROD DOM, 36(1), 2001, pp. 41-45
The dynamics of prolactin (PRL) and luteinizing hormone (LH) secretion in t
he anoestrous bitch is poorly known. Therefore, the objective of this study
was to characterize the 24 h profiles of serum PRL and LH in crossbred ano
estrous bitches and to assess whether a relationship exists between the sec
retory patterns of these two hormones. Serum PRL and LH concentrations were
measured in 10 healthy anoestrous crossbred bitches at 145 min intervals f
or 24 h. During the experiment the animals received continuous artificial i
llumination and remained undisturbed except at the time of blood sampling.
Serum PRL was measured by a homologous enzyme-linked immunosorbent assay, w
hereas LH and progesterone (P-4) were determined by radioimmunoassay. The a
noestrous state of the bitches was assessed by vaginal cytology, vaginoscop
y and physical examination. Two groups of animals were identified according
to their PRL levels: a high PRL group (n=3, mean +/- SEM 12.3 +/- 2.7 ng/m
l) and a low PRL group (n=7, mean +/- SEM: 2.5 +/- 0.9 ng/ml). In the low P
RL group, the PRL profiles were flat and did not show any significant circa
dian pattern. Nevertheless, occasional single-point peaks were detected in
some of the bitches. In the high PRL group the individual PRL profiles were
variable. To detect the presence of a circadian change of PRL concentratio
ns, two different sets of time windows (TW) of sampling were studied. The f
irst set was: day [TW1A, samples 1-5 (0900-1840 h)] and night [TW1B, sample
s 6-10 (2105-0645 h)]. The second set was chosen after visual inspection of
the average PRL profiles for both (high and low) groups: [TW2A, samples 3-
7 (1350-2330 h) and TW2B, samples 1-2 and 8-10 (0155-1125 h)]. PRL concentr
ations were not significantly different between day and night. In the high
PRL group, but not in the low PRL group, average serum PRL was significantl
y(p < 0.01) higher in TW2A than TW2B. In both groups serum LH levels were m
ore homogeneous than PRL levels. Neither TW showed circadian changes in LH
patterns of secretion (TW1A versus TW1B, p < 0.69; TW2A versus TW2B, p < 0.
88). On the other hand, bitches in the high PRL group showed significantly
(p < 0.01) lower serum LH levels than those in the low PRL group of animals
. Serum PRL concentrations presented a significant inverse correlation with
LH concentrations (r=-0.21, p < 0.03) and a significant positive correlati
on with Pq concentrations across the study (0.92, p < 0.01). It is conclude
d that in anoestrous crossbred bitches serum PRL is highly variable and inv
ersely related to LH. No circadian rhythm of PRL secretion appears to exist
in most anoestrous bitches.