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Pre-
and neonatal control of pituitary hormone secretion in the pig
by N. Parvizi
No
abstract available. Two chapters are given in full lengh
together with the headings for the whole article.
Pituitary
GH secretion
Growth hormone is visible in the pituitary at a very early stage
of fetal development in the pig. Shortly after the appearance
ofsomatotrope cells, around day 35-40 p.c. (post coitum) GH
can be measured using immunohistochemistry or radioimmunoassay.
On day 80 p.c. a level fifty times higher than that on day 40
p.c. is measurable (Klindt & Stone 1984). A further increase
is obvious between days 70 and 90 p.c. (DeHoffet al. 1986; Lee
et al. 1993).
Basal GH secretion
We studied the basal GH secretion in chronically catheterized
pig fetuses from day 89 of gestation to parturition and in neonates
from birth to day 25 posmatally. In the pig, like in most other
mammalian species (ovine: Gluckman et al. 1979; bovine: Coxam
et al. 1988; human: Lanes et al. 1989) GH levels are higher
in fetuses than in their mothers (fetal pig: x = 50 ±
10 ng/ml; sow = 2.2 ± 1.0 ng/ml).
Growth hormone secretion undergoes ontogenetic changes in male
fetuses. Plasma GH concentrations are significantly higher at
94 - 98 days p.c. compared with other fetal ages (Fig. 1). The
increase is due to an enhancement of amplitude of GH pulses
(Fig. 2). A sharp decline in GH levels is apparent shortly before
birth which is statistically significant in male fetuses (Bauer
& Parvizi 1996). These sex differences in secretory patterns
ofGH are most probably a reflection of ontogenetic changes at
the level of GH gene expression in the pituitary (Granz et al.1997).
Insulin-like groth factor 1 (IGF-1) levels in plasma are, in
contrast to earlier reports (Lee et al. 1991), considerably
higher in fetuses than in the dam (Fig. 1). There are no ontogenetic
alterations in IGF-1 secretion in both genders. But, likewise
GH IGF-1 levels are at maximum in males around days 94-98 p.c.
It is worth mentioning that maternal plasma IGF-1 levels increase
linearly with progressing gestation. Fetal and maternal IGF-1
and GH release do not possess any diurnal rhythmicity. Both
hormones, IGF-1 as well as GH, are released in a highly pulsatile
manner in the fetus. In dams, however, IGF-1 release remain
constant during a 24h period and does not show any significant
fluctuations.
Neurohormonal
control of GH secretion (Fig. 1, 2)
Opioidergic
control of GH secretion (Fig. 3)
Pituitary
LH secretion
Opioidergic
control of LH secretion (Fig. 4, 5)
Effects
of cytokines on LH secretion (Fig. 6)
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