Effect of somatostatin on prolactin in rainbow trout (Oncorhynchus mykiss) pituitary cells in primary culture

Abstract

To study the control of prolactin secretion in fish, an in-vitro technique using a monolayer cell culture system of rainbow trout pituitary glands was developed. Such secretion was characterized by measurement of both prolactin release and prolactin mRNA content using a trout prolactin cDNA as a probe. This cell culture technique, already used to study the regulation of gonadotrophin secretion in rainbow trout, was further validated by measuring total DNA and protein content. Both parameters appeared to be stable after 2 days of culture. Studying the effect of somatostatin (SRIF) on prolactin cells indicated that a maximal inhibitory effect (62%) was observed after 24 h of treatment. Significant inhibition of prolactin release was obtained for SRIF doses ranging from 50 nM to 1 microM. However, in the same experiment, SRIF was much more potent as an inhibitor of growth hormone release. Short-term (< 12 h) incubation with SRIF did not induce a significant change in prolactin release, whereas growth hormone release was reduced at as early as 1 h after SRIF exposure. SRIF did not have a significant effect on total prolactin content or prolactin mRNA levels, suggesting the absence of an effect on prolactin synthesis. No increase in the magnitude of the inhibitory effect of SRIF was observed when using pituitary cells from immature, mature male or mature female trout. When comparing effects on primary cultures containing cells from the whole pituitary with a prolactin cell-enriched population, SRIF appeared to have the same inhibitory effect on prolactin release, supporting a direct action of SRIF on prolactin cells. These results provide further support for SRIF being a prolactin-inhibiting factor in rainbow trout and acting as a modulator of a dominant stimulatory control of prolactin release.

GABA-ergic control of prolactin release in rainbow trout (Oncorhynchus mykiss) pituitaries in vitro

“…Shorter periods of exposure to GABA were tested without leading to significant effect on PRL release. Such delay in the response of trout PRL cells in primary culture has already been described when studying the effects of somatostatin (Le Goff et al 1992). This situation, not observed with GH cells, was suggested by Le Goff et al (1992) to be associated with a particular behaviour of cultured PRL cells which seem to be under a dominant stimulatory control by hypothalamus in rainbow trout (Gonnet et al 1989;Yada et al 1991).…”

“…The procedures for preparing dispersed and cultured cells from rainbow trout pituitary glands have already been described in details by Weil et al (1986) and Le Goff et al (1992). In these series of culture experiments, pre-treatment with poly-Llysine (Sigma Chemical Company, 5 g/cm 2 ) was applied to culture plates before cell plating.…”

Development and characterization of five rainbow trout pituitary single-cell clone lines capable of producing pituitary hormones

“…This step can be difficult to reproduce consistently, and the dissociated cells frequently require a period of time to recover, during which the expression of certain genes could be detrimentally affected. For instance, as reported by Le Goff et al (1992), the expression of prl gene in the rainbow trout primary pituitary cell cultures dropped significantly during the first 2 days of the cultures. Additionally, primary pituitary cell cultures can only be maintained for 1 week; new cultures need to be prepared in order to repeat any experiment.…”

“…Whole pituitary gland cultures (Yada et al 1991, Elango et al 2006 and dissociated pituitary gland primary cell cultures (Le Goff et al 1992) are the two in vitro systems that have been used to study factors that regulate the production and secretion of GH and prolactin (PRL) in the pituitary of rainbow trout (Oncorhynchus mykiss). Both systems are considered short term, with cultures usually only being able to be maintained for about 1 week.…”

Isolation and culture of somatotrophs from the pituitary of the rainbow trout: Immunological and physiological characterization

“…A partial enrichment by manual dissection was tried because such a technique, using rostral pars distalis fragments, resuited in a 60% enriched prolactin cell population (Le Goff et al, 1992). Using proximal pars distalis fragments, a 40% enriched GH cell population and a 20% GtH2 cell population were obtained in the present work, showing the necessity to perform further purification to obtain a better enrichment in GH and GtH2 cells.…”