Hypophyseal-Portal Concentrations of Growth Hormone-Releasing Factor and Somatostatin in Conscious Pigs: Relationship to Production of Spontaneous Growth Hormone Pulses

Abstract

A method of collecting hypophyseal portal blood (HPB) in conscious pigs was used to show the relationship between GRF and somatostatin (SRIF) concentration and peripheral GH response. Six male castrate pigs (approximately 63 kg body weight) had HPB and jugular blood collected individually for an average of 175 min each. Twenty-seven spontaneous GH pulses were detected in the 1050 min of total HPB collection. Of the associations examined, the only significant finding was that GH pulse maxima occurred nonrandomly within periods of SRIF descent (63%; P = 0.005). Although 48% (13/27) of GH pulse maxima were associated with an ascent in portal GRF concentration, these associations were not determined to be nonrandom (P = 0.14). Only 7 of 27 (26%) GH pulse maxima were associated with an ascent in portal GRF concentration and a descent in SRIF concentration occurring simultaneously. A saline infusion given approximately 120 min after beginning blood collection resulted in an increase in SRIF pulse frequency and a decrease in GH-AUC and GRF-AUC. The cause of this saline effect is unknown, but it may have been related to acclimation of the pigs to the blood collection procedure. These data show the complexity of the relationship between SRIF and GRF concentrations and GH secretion and may indicate a close relationship with SRIF in GH pulse generation in the pig. In addition, these data support the hypothesis that, in the pig, mediation of GH release cannot be explained simply by antagonism between GRF and SRIF.

A novel stereotaxic approach to the hypothalamus for the use of push-pull perfusion cannula in Holstein calves

“…Furthermore, it was suggested that restricted feeding affected the hypothalamic control of GH secretion in sheep (Thomas et al, 1991). Drisko et al have suggested that SS has a closer relationship with GH pulses than GHRH, as determined by portal blood sampling in castrated male pigs (Drisko et al, 1998). In our study performed in intact male calves, a close relationship among these three parameters was not observed.…”

“…Pulsatile GH secretion has been observed in most species studied, including rats (Tannenbaum and Martin, 1976), humans (Finkelstein et al, 1972), monkeys (Woller et al, 2002), pigs (Drisko et al, 1998), goats (Mogi et al, 2002), sheep (Frohman set al, 1990) and cattle (Breier et al, 1986;Lee et al, 1991;Plouzek and Trenkle, 1991). GH pulses clearly occur regularly at approximately 3.3 h intervals in male rats (Tannenbaum and Martin, 1976).…”

“…Both GHRH and SS were secreted in a pulsatile manner with irregular pulse patterns. The release of GHRH and SS from the hypothalamus in vivo has been demonstrated using two different techniques in rats (hypophyseal portal blood collection) (Plotsky and Vale, 1985;Watanobe and Habu, 2002), sheep (hypophyseal portal blood collection) (Frohman et al, 1990;Magnan et al, 1993), pigs (hypophyseal portal blood collection) (Drisko et al, 1998) and most recently in monkeys (push-pull perfusion of the stalk-median eminence) (Nakamura et al, 2003). In cattle, GHRH and/or SS secretion has been determined by in vitro experiments, such as perifusion of bovine hypothalamic slices (McMahon et al, 2001a;West et al, 1997) or tissue blocks (Ogwuegbu et al, 1991), or immunocytochemistry (McMahon et al, 2001a.…”

Pulsatile growth hormone secretion persists in genetic growth hormone-releasing hormone resistance

“…This model is supported by studies using immunoneutralization of GHRH and somatostatin (65, 80), GHRH, or somatostatin antagonists (5,33,34,73), as well as direct pituitary portal sampling in experimental animals (18,20,55,66). A reciprocal relationship between GHRH and somatostatin, where GHRH pulses coincide with somatostatin troughs, has been reported in rats (37,55,65), but this pattern is less clear in sheep or pigs, where more complex relationships between oscillations in GHRH, somatostatin, and GH prevail (8,15,20,66). Thus important species as well as sex differences exist in the regulation of GH secretion.…”

Developmental Changes in the Long Form Leptin Receptor and Related Neuropeptide Gene Expression in the Pig Brain1

“…Greater hypothalamic somatostatin mRNA expression at 3.5 mo of age compared to the other ages supports the idea of an age-related decline in GH secretion related to increased somatostatin secretion. Furthermore, Drisko et al [21] reported a temporal relationship between hypophyseal-portal blood concentration of somatostatin and generation of serum GH pulses in the pig.…”