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Neuroendocrinology Letters incl. Psychoneuroimmunology & Chronobiology

 

NeuroendocrinologyİLetters
ISSNİ0172ñ780X Copyrightİ©İ1997 NeuroendocrinologyİLetters

NEL Vol. 18 No. 2/3
Original Article

1998; 18:141-152
pii: NEL182397A06

 

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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