A passive ankle dorsiflexion testing system to assess mechanobiological and structural response to cyclic loading in rat Achilles tendon.

Tendinopathy is thought to be caused by repeated overload of the tendon with insufficient recovery time, leading to an inadequate healing response and incomplete recovery of preinjury material strength and function. The etiology of tendinopathy induced by mechanical load is being explored with a variety of mechanical load scenarios in small animals. This study establishes a testing system that applies passive ankle dorsiflexion to a rat hindlimb, estimates the force applied to the tendon during cyclic loading and enables the assessment of subsequent structural and biological changes.

Regulation of prolactin receptor expression by estradiol in the female rat brain.

Prolactin (PRL) receptors have been identified in many tissues, including the brain, but little is known about their distribution and regulation. In the female rat brain, ovariectomy significantly (p < 0.05) decreased PRL binding capacity, but not the affinity, in the hypothalamus and pons-medulla.

Prolactin induced expression of interleukin-1 alpha, tumor necrosis factor-alpha, and transforming growth factor-alpha in cultured astrocytes.

Prolactin (PRL) is a potent mitogen in cultured astrocytes. Because one of the major effects of astrocyte proliferation is the expression of inflammatory cytokines, we examined the effect of PRL-induced mitogenesis on the expression of interleukin-1 (IL-1 alpha), tumor necrosis factor-alpha (TNF-alpha), and transforming growth factor-alpha (TGF-alpha) in cultured astrocytes. Astrocytes were stimulated with PRL or growth hormone (GH), and the expression of cytokines was determined by immunohistochemistry and Western blot analysis.

Prolactin-stimulated mitogenesis of cultured astrocytes is mediated by a protein kinase C-dependent mechanism.

Prolactin (PRL) has been reported to activate cellular proliferation in nonreproductive tissue, such as liver, spleen, and thymus. Recently, we have extended the possible role of PRL as a mammalian mitogen by demonstrating a mitogenic effect of PRL in cultured astrocytes. Although the cellular mechanisms by which PRL regulates cell growth are not fully understood, protein kinase C (PKC) has been implicated as one of the transmembrane signaling systems involved in the regulation of PRL-induced cell proliferation in Nb2 lymphoma cells and liver.

Estradiol increases prolactin synthesis and prolactin messenger ribonucleic acid in selected brain regions in the hypophysectomized female rat.

Immunoreactive PRL which is not of pituitary origin, has been identified in many regions of the rat brain. We have previously demonstrated that estradiol increases hypothalamic immunoreactive PRL content in hypophysectomized female rats. To determine if estradiol stimulates PRL synthesis, we examined the effect of estradiol on the in vivo production of PRL, and on the expression of PRL messenger RNA (mRNA) in the hypothalamus, pons, and cerebral cortex.

Proteolytic modification of prolactin by the female rat brain.

Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analyses we have identified immunoreactive prolactin (PRL) proteins with molecular weights of 24 and 16 kD in the female rat brain. Because PRL target tissues have been shown to contain enzymes which, in vitro, cleave PRL into a 16-kD PRL fragment, studies were performed to characterize PRL proteolysis in the female rat brain. In vitro proteolysis of PRL was examined by incubating [125]I-PRL with 25,000 g subcellular fractions followed by SDS-PAGE under reducing conditions.

Prolactin-stimulated mitogenesis of cultured astrocytes.

PRL has been reported to activate cell cycle-specific enzyme markers in nonreproductive tissues. To determine if PRL stimulates cell cycle-specific markers and cell growth in the central nervous system, the effect of PRL on cellular proliferation was examined in cultured astrocytes. Astrocytes from confluent cultures were plated onto glass slides at a density of 2 x 10(4) cell/ml 24 h before use.

Stimulation of hypothalamic prolactin release by veratridine and angiotensin II in the female rat: effect of ovariectomy and estradiol administration.

In the female rat immunoreactive prolactin (IR-PRL) has been identified in the hypothalamus and in other brain regions. Brain IR-PRL is not of pituitary origin and, based on polyacrylamide gel electrophoresis and peptide mapping, shares a high degree of sequence homology with its pituitary counterpart. We have previously shown that hypothalamic tissue can release IR-PRL in vitro when depolarized by potassium.

Prolactin stimulation of protein kinase C activity in the rat hypothalamus.

Stimulation of cultured hypothalamic slices with PRL causes a rapid translocation of a Ca2+/phospholipid dependent protein kinase from the cytosol to the membrane fraction. The translocation of PKC from the cytosol to the membrane occurred at physiological concentrations of PRL with a maximal response occurring at 10(-10) M. At concentrations above this, there was less PKC activity translocated from the cytosol to the membrane.