Maternal prolactin inhibition during lactation affects physical performance evaluated by acute exhaustive swimming exercise in adult rat offspring

Maternal prolactin inhibition at the end of lactation programs for metabolic syndrome and hypothyroidism in adult offspring, which could negatively affect exercise performance. We evaluated the effects of maternal hypoprolactinemia in late lactation on physical performance in adult progeny. Lactating Wistar rats were treated with bromocriptine (BRO, 1?mg per day) or saline on days 19, 20, and 21 of lactation and offspring were followed until 180 days old. Physical performance was recorded in untrained rats at 90 and 180 days by an acute exhaustive swimming test (exercise group-Ex). At day 90, BRO offspring showed higher visceral fat mass, higher plasma thiobarbituric acid reactive substances, lower total antioxidant capacity, higher liver glycogen, lower glycemia, and normal insulinemia. Although thyroid hormones (TH) levels were unchanged, mitochondrial glycerol phosphate dehydrogenase (mGPD) activity was lower in muscle and in brown adipose tissue (BAT). At this age, BRO-Ex offspring showed higher exercise capacity, lower blood lactate, higher serum T3, and higher muscle and BAT mGPD activities. At day 180, BRO offspring showed central obesity, hypothyroidism, insulin resistance, and lower EDL (extensor digitorum longus) muscle glycogen with unaltered plasma oxidative stress markers. This group showed no alteration of exercise capacity or blood lactate. After exercise, EDL and liver glycogen were lower, while T3 levels, BAT and muscle mGPD activities were normalized. Liver glycogen seem to be related with higher exercise capacity in younger BRO offspring, while the loss of this temporary advantage maybe related to the hypothyroidism and insulin resistance developed with age.     

Induction of Gene Expression of the Catecholamine-Synthesizing Enzymes by Insulin-Like Growth Factor-I

Abstract: The effects of insulin-like growth factor-I (IGF-I) on gene expression and the activities of the three enzymes specific for catecholamine biosynthesis, tyrosine hydroxylase (TH), dopamine β-hydroxylase (DBH), and phenylethanolamine N -methyltransferase (PNMT), were determined in bovine adrenomedullary chromaffin cells primary cultured in serum-free medium. The mRNA level of TH was maximally elevated in the presence of IGF-I by 3.1 ± 0.4-fold after 48 h, DBH by 5.1 ± 0.3-fold in 24 h, and PNMT by 2.8 ± 0.5-fold in 72 h. In addition, the activity of TH was increased by 77%, DBH by 70%, and PNMT by 23% in IGF-I-exposed cultures. In the absence of the growth factor, the mRNA levels of TH and DBH were decreased to 45 ± 10% and 35 ± 12% of the time-zero control within 48 h while PNMT mRNA was decreased to 82 ± 5% only after 72 h. When the cells were cotreated with the protein tyrosine kinase inhibitor genistein, DBH induction by IGF-I was suppressed, confirming that the effect is mediated by tyrosine kinase. Cotreatment with the protein kinase A (PKA) inhibitor H89 caused complete reversal of the IGF-I-induced DBH increase and the effects of IGF-I treatment and PKA activation by forskolin were not additive, suggesting that PKA is involved in the signaling initiated by IGF-I in these cells.     

Regulation of basal expression of catecholamine-synthesizing enzyme genes by PACAP.

We have previously reported that the cAMP/protein kinase A (PKA) pathway is important in the gene regulation of both induction and basal expressions of the catecholamine synthesizing enzymes tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH). The neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to activate the intracellular cAMP/PKA pathway. In the present study, using primary cultured bovine adrenal medullary cells, we determined whether the basal activity of the PACAP receptor might play a role in the maintenance of the basal expression of these enzyme genes via the cAMP/PKA pathway. The potent PACAP receptor antagonist PACAP (6-38) caused a reduction of TH and DBH mRNA levels in a dose dependent manner as well as their enzyme activities and TH protein level. The effects of PACAP (6-38) and the PKA inhibitor H-89 exhibited generally similar trends, and were not additive in the reduction of TH and DBH gene expression and activities, suggesting that they take a common intracellular signaling pathway. The antagonist also caused decreases in the intracellular norepinephrine and epinephrine levels similar to the effect of H-89. Taken together, the data suggests that PACAP is involved in the regulation of maintenance of the catecholamine synthesizing enzymes TH and DBH by utilizing the cAMP/PKA pathway.     

Effect of hydrocortisone on catecholamines and the enzymes synthesizing them in the developing sympathetic ganglion

Summary Newborn rats were daily injected with 0.2 mg hydrocortisone acetate for seven days. They were killed 1, 7 or 21 days after the last injection, together with untreated controls. Hydrocortisone caused a great increase in the number of the small, intensely fluorescent (SIF) cells and the appearance of similar small cells with intense immunohistochemical reactions for tyrosine hydroxylase (TH), dopamine--hydroxylase (DBH) and phenylethanolamine (noradrenaline)N-methyltransferase (PNMT) in the superior cervical ganglion. At the same time, the adrenaline content and the PNMT activity of the ganglion greatly increased, while no significant changes were observed in the dopamine or noradrenaline content or TH or DBH activity. All these changes essentially disappeared after a recovery period of seven or 21 days.It is concluded that hydrocortisone causes a temporary increase in the number of SIF cells by causing a synthesis of TH, DBH and PNMT in previously existing small, non-fluorescent cells, which start to synthesize and store adrenaline, thus becoming intensely fluorescent SIF cells. These SIF cells are different from the normal SIF cells of the same ganglion, most of which appear at a later stage of postnatal development when response to hydrocortisone is lost, which contain TH but neither DBH nor PNMT, and which permanently remain in the ganglion.     

Development of catecholaminergic phenotypic characters in the mouse locus coeruleus in vivo and in culture

While abundant studies have begun to elucidate ontogeny of the peripheral nervous system, molecular mechanisms underlying brain development remain obscure. To approach this problem, we initiated parallel in vivo and in vitro studies of the mouse locus coeruleus (l.c.), a brainstem noradrenergic nucleus. The catecholaminergic enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) were used to monitor phenotype expression and development. TH catalytic activity and immunocytochemical reactivity were initially detectable on gestational Day 13 (E-13) in vivo, and adult levels of activity were approximately by the third postnatal week. Immunotitration studies indicated that the developmental increase was due to accumulation of enzyme molecules and not enzyme activation. The in vivo developmental profile of DBH approximated that of TH. To begin defining regulatory mechanisms, explants of embryonic brainstem were placed in culture. Explantation on E-12, prior to expression of TH or DBH, resulted in the de novo appearance of these phenotypic characters after 4 days. Explantation on E-18, after the enzymes are already expressed, was followed by a striking sixfold rise in TH activity. Immunotitration studies revealed that the increase in TH activity in E-18 cultures was attributable to increased molecule number, reproducing the in vivo results. Moreover, the E-18 explants, cultured for 3 weeks, attained higher plateau levels of TH activity than E-12 cultures, and this differences was due to increased molecule number. Morphometric analysis indicated that 3-week E-12 cultures actually had more l.c. cells than E-18 cultures, indicating that differences in TH were not due to increased cells in the E-18 l.c. Finally, systemic study revealed that the development of TH activity in culture increased progressively from E-11 to E-12 to E-13, suggesting that critical regulatory events occur at this time. Our studies suggest that the l.c. is an excellent model for the study of brain development in vivo and in vitro. Initial phenotypic expression and dramatic development occur in culture in the absence of normal targets, normal afferent innervation and, presumably, normal humoural milieu.     

Cretinism: influence on rate-limiting enzymes of amine synthesis in rat brain.

The effect of neonatal hypothyroidism on tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH) activity, as well as on water content, was studied in different regions of the developing rat brain. Neonatal hypothyroidism, induced by daily treatment with propylthiouracil starting at birth, led to a cretinoid syndrome with a marked impairment of body and brain growth. Compared to control littermates, 30- and 45-day-old cretinous rats had elevated levels of water in the brain stem. The activities of TH and TPH were increased in a time-dependent manner in the brain stem, basal ganglia and hypothalamus of maturing cretinous animals. The increased activity of these rate-limiting enzymes of mono-amine synthesis may account for the elevated levels of brain norepi-nephrine and serotonin in rats subjected to neonatal hypothyroidism.     

Ganglion cells immunoreactive for catecholamine-synthesizing enzymes,neuropeptide Y and vasoactive intestinal polypeptide in the rat adrenal gland

Immunohistochemistry has been used to demonstrate tyrosine hydroxylase (TH), dopamine--hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) immunoreactivities, and acetylcholinesterase (AChE) activity was demonstrated in rat adrenal glands. The TH, DBH, NPY and VIP immunoreactivities and AChE activity were observed in both the large ganglion cells and the small chromaffin cells whereas PNMT immunoreactivity was found only in chromaffin cells, and not in ganglion cells. Most intraadrenal ganglion cells showed NPY immunoreactivity and a few were VIP immunoreactive. Numerous NPY-immunoreactive ganglion cells were also immunoreactive for TH and DBH; these cells were localized as single cells or groups of several cells in the adrenal cortex and medulla. Use of serial sections, or double and triple staining techniques, showed that all TH- and DBH-immunoreactive ganglion cells also showed NPY immunoreactivity, whereas some NPY-immunoreactive ganglion cells were TH and DBH immunonegative. NPY-immunoreactive ganglion cells showed no VIP immunoreactivity. AChE activity was seen in VIP-immunopositive and VIP-immunonegative ganglion cells. These results suggest that ganglion cells containing noradrenaline and NPY, or NPY only, or VIP and acetylcholine occur in the rat adrenal gland; they may project within the adrenal gland or to other target organs. TH, DBH, NPY, and VIP were colocalized in numerous immunoreactive nerve fibres, which were distributed in the superficial adrenal cortex, while TH-, DBH- and NPY-immunoreactive ganglion cells and nerve fibres were different from VIP-immunoreactive ganglion cells and nerve fibres in the medulla. This suggests that the immunoreactive nerve fibres in the superficial cortex may be mainly extrinsic in origin and may be different from those in the medulla.     

Parallel Up-Regulation of Catecholamine Biosynthetic Enzymes by Dexamethasone in PC12 Cells

Abstract: We sought to investigate whether dexamethasone produces a coordinated, time-dependent effect on all enzymes in the catecholamine biosynthetic pathway in PC12 cells. The levels of mRNAs of tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), and dopamine γ-hydroxylase (DBH) were examined at 0, 6, 12, 24, and 48 h after dexamethasone (5 μ M ) treatment to PC12 cells. The levels of all enzyme mRNAs steadily increased for 24 h, although the increase of AADC mRNA content was slow. The increased mRNA levels of TH and AADC were maintained at 48 h, whereas the level of DBH mRNA was sharply decreased at 48 h. The maximally induced mRNA levels were ∼5.0-, 2.4-, and 7.0-fold higher than the control levels of TH, AADC, and DBH, respectively. The elevation of enzyme activities was detected later than the increase in levels of mRNAs. The maximal activities of TH, AADC, and DBH were reached between 48 and 72 h with 3.6-, 1.8-, and 8.0-fold increases, respectively. Low, but detectable, phenylethanolamine N -methyltransferase (PNMT) activity was observed in PC12 cells, and dexamethasone increased its activity 5.6-fold at 72 h. The PNMT mRNA was easily detected by northern blot analysis after exposure for 24 h to dexamethasone. The data suggest that, in PC12 cells, dexamethasone up-regulates all catecholamine biosynthetic enzyme genes in a parallel fashion.     

Effects of Systemic Administration of 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine to Mice on Tyrosine Hydroxylase, l-3,4-Dihydroxyphenylalanine Decarboxylase, Dopamine β-Hydroxylase, and Monoamine Oxidase Activities in the Striatum and Hypothalamus

The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg/kg subcutaneously per day for 8 days) to C57BL/6N mice were studied on tyrosine hydroxylase (TH), L-3,4-dihydroxyphenylalanine decarboxylase (DDC), and monoamine oxidase (MAO) activities in the striatum, and TH, DDC, dopamine-beta-hydroxylase (DBH), and MAO activities in the hypothalamus. Treatment with MPTP led to a large decrease in TH activity and a parallel decrease in DDC activity in the striatum, as compared with the saline controls. In contrast, MPTP administration did not cause a decrease of the activities of TH, DDC, and DBH in the hypothalamus. There was also no reduction in MAO activities of striatum and hypothalamus. These data indicate that MPTP administration to mice results in specific degeneration of the dopaminergic nigrostriatal pathway and that DDC in the mouse striatum may mainly be localized in the dopaminergic neurons with TH.     

Quantitation of changes in gene expression of norepinephrine biosynthetic enzymes in rat stellate ganglia induced by stress

Enzymes involved in catecholamine synthesis are present in the highest concentration in the adrenal medulla, however they were found also in other, mainly nervous tissues. The aim of our study was to quantify the exact concentration of tyrosine hydroxylase (TH) and dopamine-ss-hydroxylase (DBH) mRNA in rat stellate ganglia under control conditions and at different intervals after exposure to immobilization stress (IMO). In rats immobilized once for 2h, we determined TH and DBH mRNA in different time intervals up to 22 h after the end of the stress stimulus. TH immunoreactive protein levels were also determined in stellate ganglia. TH and DBH mRNA levels were quantified by RT-competitive-PCR.In stellate ganglia, the concentration of TH mRNA was 17+/-1.6 amol/microg of total RNA, which is approximately 30-times lower than in the adrenal medulla. The concentration of DBH mRNA in the stellate ganglia was 2601+/-203 amol/microg of total RNA, which is the concentration similar to adrenal medulla, but is 150-times higher than concentration of TH mRNA in stellate ganglia. After a single 2-h immobilization the highest elevation of TH and DBH mRNA levels was measured 22 h after the termination of the stress stimulus. Repeated immobilization (7 days, 2h daily) did not produce further increase in TH and DBH mRNA levels compared to already elevated levels in adapted control group (immobilized for 6 days, 2h daily and decapitated 22 h later). Levels of TH protein were significantly changed only after the repeated immobilization.This study compared for the first time the precise amounts of TH and DBH mRNA in rat stellate ganglia under control conditions and after immobilization stress, and indicates large differences in their concentration. TH and DBH mRNA concentrations in stellate ganglia are markedly elevated for a prolonged period of time after termination of the stress stimuli.     

Intrinsic choroidal neurons in the duck eye receive sympathetic input: anatomical evidence for adrenergic modulation of nitrergic functions in the choroid

Intrinsic choroidal neurons (ICN) in the duck eye form an intramural ganglionic plexus that may subserve complex integrative functions. A key feature of such ganglia is an innervation by sympathetic postganglionic neurons. The present study was thus aimed at determining the sympathetic postganglionic innervation of ICN. Choroids were processed for double immunofluorescence labelling with the following markers: tyrosine-hydroxylase (TH)/nitric oxide synthase (nNOS), TH/galanin (GAL), dopamine-beta-hydroxylase (DBH)/vasoactive intestinal polypeptide (VIP), TH/DBH and DBH/alpha-smooth-muscle actin (alphaSMA), and for triple immunofluorescence labelling with VIP/DBH/TH. Epifluorescence and confocal laser scanning microscopy were used for evaluation. Immunoperoxidase staining for TH or DBH in combination with NADPH-diaphorase histochemistry was applied for electron microscopy. ICN spread over the entire choroid but were concentrated in an equatorial zone passing obliquely from naso-cranial to temporocaudal. More than 80% of nNOS-positive ICN showed close appositions of TH/DBH-immunoreactive varicose nerve fibres at the light-microscopic level, as could be confirmed by confocal laser scanning microscopy. Ultrastructurally, these appositions could be defined as both synapses or close contacts without synaptic specialisation. Vascular and non-vascular smooth muscle fibres also received TH/DBH-immunopositive innervation. Our findings suggest that most ICN receive a sympathetic input that might modulate their nitrergic effects upon vascular and non-vascular smooth muscle fibres in the choroid and that they may have more complex functions than merely being a simple parasympathetic relay.     

Increased gut-derived norepinephrine release in sepsis: up-regulation of intestinal tyrosine hydroxylase

Studies have shown that increased gut-derived norepinephrine (NE) release plays an important role in producing hepatocellular dysfunction at the early stage of sepsis. Although the gut has been demonstrated to be the major source of NE in sepsis, it remains unknown whether the increased NE is associated with up-regulation of intestinal NE biosynthesis enzymes such as tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH). To determine this, adult male rats were subjected to sepsis by cecal ligation and puncture (CLP) followed by fluid resuscitation. Small intestinal samples were harvested at 2 h (i.e., early sepsis) or 20 h (late sepsis) after CLP or sham-operation. Protein levels of TH and DBH were determined by Western blot analysis and immunohistochemistry. Their gene expression was assessed by RT-PCR technique. The results indicate that intestinal TH protein levels increased significantly at 2 and 20 h after CLP, while DBH was not altered under such conditions. Immunohistochemical examination shows that both TH and DBH were located in intestinal sympathetic nerve fibers and TH staining was markedly increased in septic animals. TH gene expression increased significantly at 2 h but not at 20 h after CLP, while DBH gene expression was not altered in sepsis. Thus, the increased TH gene and protein expression appears to be responsible for the increased gut-derived NE in sepsis.     

A study of selected catecholamine metabolizing enzymes: a comparison of depressive suicides and alcoholic suicides with controls

—The regional distributions of monamine oxidase (MAO) (EC 1.4.3.4), catechol-O-methyltransferase (COMT) (EC 2.1.1.6), tyrosine hydroxylase (TH) (EC 1.14.3.2), and dopamine-β-hydroxylase (DBH) (EC 1.14.2.1) have been examined in human brains obtained at autopsy from persons who died of natural causes (controls), and from persons who committed suicide and were further categorized as suffering from affective disorder (depression) or from alcoholism. Post mortem animal studies showed no changes in MAO or COMT activities in rabbit brain or in DBH activity in rat brain when the intact bodies were left at room temperature up to 24 h. TH activity in rabbit brains, however, began to decline immediately after death and after 24 h at room temperature it was approximately 48 per cent of the fresh brain level. There was no significant variation in activity of COMT, TH and DBH in human brain attributable to age or sex. MAO activities in the 60–70 yr decade were 34 per cent higher than in the 30–40 yr decade. MAO activities were highest in the hypothalamus and substantia nigra, TH activities were highest in substantia nigra, putamen and head of caudate, and DBH activities were greatest in tegmentum of pons and hypothalamus. Only minimal regional differences in COMT activities were observed. No significant differences were found between enzyme activities in brain areas of controls and suicides with the possible exception of TH in the substantia nigra, where the depressive suicides (but not the alcoholics) showed greater activity (P < 0·02). These findings appear not to support the catecholamine hypothesis of affective disorder.     

Differentiation of adrenomedullary catecholamine synthesizing enzyme responses to repeated immobilization in hybrid rats

The response of adrenomedullary catecholamine synthesizing enzymes to repeated immobilization was studied in hybrid (F₁) offspring of 2 inbred rat strains (LEW and F344). Immobilization-induced increases in tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyl-transferase (PNMT) activities in one of the parental strains (F344) previously were shown to be dependent upon intact adrenal gland innervation but independent of the pituitary gland, while responses in the other parental strain (LEW) were independent of adrenal innervation but dependent upon pituitary function. Factors determining immobilization-induced increases in adrenal enzymes of F₁ offspring were enzyme-specific. Increased PNMT activity was pituitary dependent in F₁ rats, whereas increased TH and DBH activities after immobilization were dependent upon an intact adrenal gland innervation. These results suggest that the factor(s) regulating PNMT responses are differentiable from those regulating TH and DBH responses. The results also indicate that analysis of PNMT responses to immobilization in backcross populations is feasible, and could indicate whether strain-specific response mechanisms are heritable.     

Central stimulatory effect of leptin on T3 production is mediated by brown adipose tissue type II deiodinase

To assess whether intracerebroventricular leptin administration affects monodeiodinase type II (D2) activity in the tissues where it is expressed [cerebral cortex, hypothalamus, pituitary, and brown adipose tissue (BAT)], hepatic monodeiodinase type I (D1) activity was inhibited with propylthiouracil (PTU), and small doses of thyroxine (T4; 0.6 nmol. 100 g body wt(-1). day(-1)) were supplemented to compensate for the PTU-induced hypothyroidism. Two groups of rats were infused with leptin for 6 days, one of them being additionally treated with reverse triiodothyronine (rT3), an inhibitor of D2. Control rats were infused with vehicle and pair-fed the amount of food consumed by leptin-infused animals. Central leptin administration produced marked increases in D2 mRNA expression and activity in BAT, changes that were likely responsible for increased plasma T3 and decreased plasma T4 levels. Indeed, plasma T3 and T4 concentrations were unaltered by central leptin administration in the presence of rT3. The additional observation of a leptin-induced increased mRNA expression of BAT uncoupling protein-1 suggested that the effect on BAT D2 may be mediated by the sympathetic nervous system.     

The expression of dopamine beta-hydroxylase, tyrosine hydroxylase, and Phox2 transcription factors in sympathetic neurons: evidence for common regulation during noradrenergic induction and diverging regulation later in development

During differentiation of sympathetic neurons in chick embryos, tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) mRNAs become detectable during the same developmental period and are both induced by BMP 4. Later during sympathetic ganglion development, DBH is detectable in TH-positive and -negative cells. Moreover, BMPs reduce DBH mRNA in cultures of sympathetic neurons while leaving TH unaffected. The data provide evidence for a common regulation of TH and DBH early during sympathetic neuron differentiation and indicate that BMPs promote their initial expression but not the maintenance during later development. The time course of Phox2a and 2b expression suggests an evolutionary conserved role in noradrenergic induction. In addition, Phox2a, Phox2b, and c-ret may be involved in the differentiation of cholinergic sympathetic neurons.     

In vitro translation of human pheochromocytoma messenger RNAs: characterization of tyrosine-hydroxylase and dopamine-beta-hydroxylase

mRNAs extracted from human pheochromocytoma were translated in vitro in a lysate of a rabbit reticulocytes. Two enzymes of the biosynthetic pathway of the catecholamines, tyrosine-hydroxylase (TH) and dopamine-beta-hydroxylase (DBH), were characterized as translation products after immunoprecipitation by specific antisera and electrophoretic analysis. The precursor of TH is a polypeptide having a molecular mass of 62,000 identical to that found for the mature protein. The molecular mass of the precursor of DBH 73,000 while that of the mature form is 79,000. TH and DBH have been translated from mRNAs having sedimentation coefficients of 22S and 25S, respectively.     

Immunocytochemical study of tyrosine hydroxylase and dopamine β-hydroxylase immunoreactivities in the rat pancreas

An immunohistochemical and immunoelectron microscopic study was used to demonstrate tyrosine hydroxylase (TH) and dopamine -hydroxylase (DBH) immunoreactivities in the rat pancreas. Small TH immunoreactive cells were found in close contact with large TH immunonegative ganglion cells among the exocrine glands and were occasionally found in some islets. Some of these TH immunoreactive cells were also DBH immunopositive. The immunoreaction product was seen diffusely in the cytoplasm and in the granule cores of TH immunoreactive cells. All intra-pancreatic ganglion cells were immunoreactive for DBH, but not for TH. The TH immunoreactive cells were identified as small intensely fluorescent (SIF) cells due to their localization and morphological characteristics and showed no insulin, glucagon, somatostatin or pancreatic polypeptide immunoreactivities. These results indicate that SIF cells may release dopamine or noradrenaline to adequate stimuli while the intra-pancreatic ganglion cells with only DBH may not synthesize catecholamines in a normal biosynthetic pathway. TH immunoreactive nerve bundles without varicosities and fibers with varicosities, associated or unassociated with blood vessels, were found in both the exocrine and endocrine pancreas. Close apposition of TH immunoreactive nerve fibers to the smooth muscle and endothelial cells of the blood vessels was observed. A close apposition between TH immunoreactive nerve fibers and exocrine acinar cells and islet endocrine cells was sometimes found in the pancreas. The immunoreaction product was seen diffusely in the axoplasm and in the granular vesicles of the immunoreactive nerve fibers. Since no TH immunoreactive ganglion cells were present in the rat pancreas, the present study suggests that noradrenergic nerve fibers in the pancreas may be extrinsic in origin, and may exert an effect on the regulation of blood flow and on the secretory acitivity of the acinar cells, duct cells and endocrine cells.